Dr Dan Bompa

Senior Lecturer in Civil and Structural Engineering / CEE Structures & Materials Lab Lead
PhD CEng MIStructE EurIng FHEA
+44 (0)1483 683390
25 AA 02
Book a meeting here: https://bit.ly/dvbompa
Open to PhD applications in hybrid structural systems, extreme loading and low carbon design.

Academic and research departments

Department of Civil and Environmental Engineering.



Research projects



A. Chira, A. Puskás, D. V. Bompa (2023)Load-deformation response of long span prestressed concrete wide beams, In: Journal of Building Engineering65 Elsevier Ltd

This paper examines the full deformational response of prestressed wide beams. The results from full-scale prestressed wide beam tests are used to validate the nonlinear numerical modelling procedures adopted in this paper. Three-dimensional modelling with detailed representation of the prestressing action is used to evaluate the response including strain distributions within the member. Simplified sectional models are also validated against the tests and detailed modelling, and are further used for an extensive parametric investigation. The parameters examined in the study include the section size, amount of non-prestressed and prestressed reinforcement, concrete strengths, and member spans. The numerical results enabled a direct assessment of the full behaviour including the forces and deflections at initial camber, cracking and ultimate state. It is shown that modelling approaches were able to predict well the overall deformation and failure modes, with the three-dimensional approach giving a more detailed insight into the internal strain distributions. Parametric studies showed that the reinforcement ratio has the greatest influence on the overall behaviour, governing the post-cracking response, compared with other parameters varied. Based on the findings, design-oriented expressions are proposed to evaluate the cracked stiffness and ultimate state deflection of prestressed wide beams. These expressions are shown to offer a reliable and practical approach for assessing the full response of such members. •Prestressed wide beams have a bi-linear response characterised by initial camber, cracking and ultimate state.•Three-dimensional and sectional modelling approaches predict well the overall deformation and failure modes.•The influence of prestressed and non-prestressed reinforcement ratio, concrete strength and member span on the response was studied.•The proposed expressions offer a reliable and practical approach for assessing the full response.

Ahmad Bakkar, A Elyamani, Adel El-Attar, D. V. Bompa, Ahmed Y. Elghazouli, Sherif Mourad (2023)Dynamic Characterisation of a Heritage Structure with Limited Accessibility Using Ambient Vibrations, In: Buildings (Basel)13(1) MDPI AG

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was created based on available architectural, structural, and material documentation to obtain detailed insight into the dominant modes of vibration. The free vibration analysis of the numerical model identified the dynamic properties of the structure using reasonable assumptions on boundary conditions. System identification, which was carried out using in situ dynamic investigation tests and input from modelling, captured three experimental natural frequencies of the structure with their mode shapes and damping ratios. The approach proposed in this study informs and directs structural restoration for the mausoleum and can be used for other heritage structures located in congested historic sites.

M Elzeadani, D. V. Bompa, A Y Elghazouli (2023)Monotonic and cyclic constitutive behaviour of rubberised one-part alkali-activated concrete, In: Construction & building materials368
C Zúñiga-Olvera, D Valverde-Burneo, N Garcia-Troncoso, C E Silva, D Gomez, D V Bompa (2022)Comparative study of the cost and behavior of RC special moment frame buildings with drop and hidden beams subjected to seismic loads, In: Front. Built Environ81032643

This study presents a comparative analysis between two structural design ideas in the Ecuadorian construction market: hidden vs. drop beams. Due to its location in a high seismic zone, structural design considerations in Ecuador must be made with care. Therefore, to offer improved strength to seismic forces, special moment frames are the most common structural system used. However, hidden beams are popular in low story buildings because of a notion of a cheaper system, despite evidence of collapse during earthquake events. In this study we look at special moment frames using hidden type and drop type beams, in terms of cost, structural, and seismic performance. A total of 32 structural models are analyzed, out of which 16 are models of buildings containing hidden beams and another 16 are drop beams. Linear and nonlinear static analysis, nonlinear local analysis, and moment curvature analysis of the modeled structures are performed to compare their seismic behavior. The structural design is carried out based on linear static analysis to obtain the total cost of all models. Additionally, a nonlinear static pushover analysis was conducted to assess roof displacement. The evidence shows that when using hidden beams, roof displacement is 20%–55% higher than when using drop beams, despite the nearly negligible differences in terms of cost. The evidence also shows that structures with drop beams, have a 22%–28% higher nominal flexural moment than structures with hidden beams, while achieving a 27%–31% higher curvature ductility. This research shows evidence on how structures with drop beams have a better behavior in high seismic risk zones when compared to structures with hidden beams, whose use although allowed, should be limited. KEYWORDS reinforced concrete beams, pushover analysis, equivalente linearization, moment-curvature relationship, seismic design

A. Y. Elghazouli, A A. Mujdeci, D. V. Bompa, Y. T. Guo (2022)Experimental cyclic response of rubberised concrete-filled steel tubes, In: Journal of Constructional Steel Research199107622

This paper examines the behaviour of circular steel tubes infilled with concrete incorporating recycled rubber particles. The rubberised concrete-filled steel tubes are tested under lateral cyclic deformations with and without co-existing axial loading. A detailed account of the cyclic tests on twelve specimens is provided together with complementary material and section tests. The rubber replacement ratio is varied up to a relatively high value of 60%, under axial loads reaching up to 30% of the nominal capacity. Hollow steel members are also tested for comparison purposes. The experimental results are discussed in detail with respect to the member stiffness, capacity, ductility, energy dissipation and failure mechanisms. Although high rubber ratios lead to a considerable loss in concrete strength, the test results show that the corresponding reduction in member capacity is much less significant due to the contribution of the steel tube and the comparatively high confinement effects mobilised within the rubberised concrete. In comparison with the members incorporating normal concrete, the rubberised concrete members are found to exhibit up to about 10% and 17% increase in ductility and energy dissipation, respectively, depending on the rubber content. Analytical treatments are then used to suggest simplified relationships for predicting the stiffness, moment-axial strength interaction, plastic hinge length and local ductility criteria. Overall, the test results demonstrate the favourable inelastic cyclic performance of circular steel tubes infilled with rubberised concrete and provide valuable experimental data. The proposed expressions for key response parameters also offer the basis for developing practical assessment and design methods.

A Mujdeci, Y Guo, D V Bompa, A.Y. Elghazouli (2022)Axial and bending behaviour of steel tubes infilled with rubberised concrete, In: Thin-Walled Structures181110125 Elsevier

This paper presents an experimental and numerical study into the behaviour of rubberised concrete-filled steel tubes (RuCFST), incorporating concrete with relatively high rubber replacements of up to 60% of mineral aggregates by volume. Axial compression, eccentric compression, and three-point bending tests on circular specimens are carried out and the results are used to validate the nonlinear procedures adopted in continuum finite element (FE) models of RuCFST members. A constitutive material model specific for confined rubberised concrete and associated modelling techniques, developed from existing procedures for concrete-filled steel tubes (CFST), is proposed for RuCFST members. The modelling techniques involve different damage definitions including low strength concrete with high rubber replacements in compression and bending. It is shown that the proposed modelling procedures can predict reliably the structural behaviour of circular RuCFST members under combined axial-bending conditions. The numerical procedures are then employed in undertaking a detailed parametric assessment for RuCFST cross-sections. The results are used to appraise current design procedures and to propose modifications that provide improved capacity predictions for a wide range of properties and loading conditions.

M Elzeadani, D V Bompa, A.Y. Elghazouli (2022)Experimental assessment and constitutive modelling of rubberised One-Part Alkali-Activated concrete, In: Construction and Building Materials353129161 Elsevier

This study deals with the development and assessment of rubberised one-part alkali-activated concrete. An experimental programme, focusing on optimising the material proportions for high flowability and compressive strength, is firstly described. This includes varying the proportions of aluminosilicate precursors, binder-to-aggregate ratio, activator dosage, and admixture quantity to find an optimum mix design with stable strength development up to 90 days. Crumb rubber particles are then added to replace up to 60 % by volume of the natural mineral aggregates. The effect of rubber addition on the mechanical properties is quantified and analytical expressions for the compressive strength, elastic modulus, splitting tensile strength, and flexural strength are presented. A database consisting of 241 conventional rubberised concrete as well as 57 rubberised alkali-activated mixes, available in the literature, is then assembled and used for direct comparison of the characteristics of different rubberised concrete materials. It is shown that the degradation in compressive strength for one-part rubberised alkali-activated concrete with high rubber replacement ratios falls within similar ranges as conventional and two-part alkali-activated rubberised concrete. However, the results show that the elastic modulus of one-part rubberised alkali-activated concrete is significantly lower than that of rubberised concrete mixes with the same compressive strength. Moreover, while the lateral crushing strain of one-part rubberised alkali-activated concrete increases with higher rubber replacement ratios, the axial crushing strain reduces slightly. It is also shown that the post-peak stress–strain response exhibits greater softening with higher rubber ratios. Based on the findings of the study, constitutive models for representing the compressive stress–strain response and flexural stress-crack width response are proposed. The presented expressions provide insights into the fundamental mechanical properties of rubberised one-part alkali-activated concrete, hence paving the way for their potential use in structural members, particularly those requiring higher ductility, while also offering a sustainable alternative to conventional concrete materials.

Mohamed Elzeadani, Dan Bompa, Ahmed Y. Elghazouli (2022)Mechanical properties and stress-strain response of rubberised one-part alkali-activated concrete, In: Proceedings of the 14th fib International PhD Symposium in Civil Engineering

This study investigates the effect of crumb rubber replacement of natural aggregates on the mechanical properties and stress-strain response, both monotonic and cyclic, of rubberised one-part alkali-activated concrete. The aluminosilicate precursors used are blast furnace slag (80%) and fly ash (20%), and the solid activator employed is sodium metasilicate anhydrous. Crumb rubber particles are used to replace both the fine and coarse natural aggregates by up to 60 vol.%, and the effect of such replacement on the compressive strength, splitting tensile strength, and flexural strength, is investigated. The monotonic and cyclic stress-strain responses of the rubberised specimens are also investigated. The results show a deterioration in mechanical properties as a function of rubber replacement of natural mineral aggregates. The elastic modulus and axial crushing strain also reduce with higher crumb rubber addition, while the descending stress-strain response shows higher softening with greater rubber replacement of natural aggregates. The normalized crushing energy and ductility of the rubberised mixes are observed to increase with higher crumb rubber replacement. The cyclic stress-strain response of the rubberised specimens falls within the monotonic stress-strain curves. The unloading modulus reduces with higher axial strain, whereas the plastic strain increases with higher axial strain indicating compressive damage accumulation with the increase in loading/unloading cycles.

A Y Elghazouli, D V Bompa, S A Mourad, A Elyamani (2022)Seismic performance of heritage clay brick and lime mortar masonry structures, In: Progresses in European Earthquake Engineering and Seismo: Third European Conference on Earthquake Engineering and Seismology – Bucharest, 2022 Springer

This paper summarises recent investigations into the structural and material response of ambient-dry and wet clay-brick and lime-mortar masonry elements, with focus on those used in heritage structures in Historic Cairo. In addition to cyclic tests on large-scale masonry walls subjected to lateral displacement and compressive gravity loads, the studies included complementary tests on small scale masonry panels and material specimens. It is shown that moisture can have a notable effect on the main material properties, including the shear and compression strengths, brick-mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses and can lead to a loss of more than a third of the stiffness and strength in addition to a reduction in ductility. Simple and cost-effective strengthening techniques, using textile-reinforced meshes, for enhancing the lateral performance of low-strength heritage masonry element, are also considered in this study. The effectiveness of the strengthening approach is illustrated and quantified through additional tests on the small-scale panels and large-scale wall specimens. It is shown that simple analytical assessment methods can be reliably adapted for predicting the response of the wall specimens, in terms of the lateral stiffness, strength and overall load-deformation behaviour.

This investigation examines the numerical cyclic response of historic masonry elements consisting of clay brick and lime mortar. The nonlinear procedures adopted for modelling the in-plane response of masonry panels under diagonal compression, as well as large walls under reverse lateral cyclic displacement and gravity load, are described. The numerical models are validated against the results of tests carried out under both dry and wet conditions which quantify the influence of moisture on the main response characteristics of the structural members. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. The numerical kinematics and stress distributions at failure are also found to be in good agreement with the test results including similar ultimate crack patterns. Overall, it is concluded that numerical models employing surface-based cohesive-contact approaches with due account for inelastic damage for modelling masonry interfaces, and damage-plasticity models to represent the constitutive behaviour of brick materials, can capture reliably the main structural response and failure modes.

This paper examines the response of reduced beam section (RBS) beam-to-column connections, through detailed nonlinear numerical assessments validated against four tests with distinct structural and geometry parameters. After describing the main test response parameters and failure modes, the modelling procedures and numerical results are presented. It is shown that three-dimensional models incorporating solid elements assigned with plastic multilinear kinematic hardening material representations can predict reliably the stiffness, strength, and overall hysteretic response. The modelling procedures adopted were also able to capture local buckling, out-of-plane connection bending and overall deformations. To verify the numerical response, the plastic strain development versus the number of cycles was assessed for the main connection components and compared with established plastic strain-life, local buckling, and ultimate plastic rotation criteria. It is shown that this approach can be used to estimate the sequence of failure and potential weld fracture, in conjunction with the load-displacement and joint strain maps. The procedures adopted in this paper can be used to reliably assess the performance of RBS connections, enabling future nonlinear parametric studies for such configurations.

Dan V. Bompa, T Bogdan, A Y Elghazouli, E Nunez, M Eatherthon, R Leon (2022)Nonlinear numerical assessment of steel reduced beam section connections., In: STESSA 2022: Proceedings of the 10th International Conference on Behaviour of Steel Structures in Seismic Areaspp. 252-260

Cyclic tests on Reduced Beam Section (RBS) connections made of heavy structural sections provided detailed insight into the structural behaviour, including strength, ductility, and failure modes of such configurations. The experimental results indicated that geometrical and material effects need to be carefully considered when designing welded RBS connections incorporating large steel profiles. To better interpret the experimental results, nonlinear finite element simulations are conducted for the test series, comprising four large-scale specimens with distinct sizes. It is shown that the numerical models can reproduce the overall moment-rotation curves, inelastic distribution, as well as failure modes. The findings point out the need, in relatively large sections with thick flanges, for a deeper RBS cut than currently specified in design guidance. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-column welds.

D. V. Bompa, B. Xu, O. Corbu (2022)Evaluation of one-part slag – fly ash alkali activated mortars incorporating waste glass powder, In: Journal of Materials in Civil Engineering

This paper describes an experimental investigation into the properties of ambient cured one-part alkali activated materials (AAMs). Mixes incorporating waste glass (WG), ground granulated blastfurnace slag (GGBS), fly ash (FA), and sodium metasilicate pentahydrate were assessed in terms of workability, water absorption, physical and mechanical properties and environmental impact. Microstructure investigations on selected mixes were also carried out. The GGBS only mixes had low workability, high early strength that declined over time, whilst FA only mixes had virtually no strength. Equal proportions of WG and GGBS provided similar fresh properties to those of GGBS mixes yet comparatively higher strengths and a positive strength time gradient. Mixes incorporating 50% GGBS, 25% FA and 25% WG, had the best balance between mechanical properties and workability, with compressive strengths above 40 MPa suitable for structural applications. An increase in activator content from 14% to 21% enhanced the strengths by 39.1%-54.6%. The flexural strengths were largely proportional to the compressive strengths, the water absorption properties were like those of cement mortars, and dry densities depended on the proportions of the constituent binders. Finally, the AAM mixes had between 53-72% less embodied carbon compared to a corresponding cement mortar.

Y. T. Guo, D. V. Bompa, A. Y. Elghazouli (2022)Nonlinear numerical assessments for the in-plane response of historic masonry walls, In: Engineering Structures268114734

This study examines the in-plane cyclic response of historic masonry elements using a micro modelling approach that incorporates damage-plasticity and surface-based cohesive-contact interface approaches. The nonlinear procedures adopted are validated against tests on dry and wet panels in diagonal compression and large walls under reverse shear-compression loading. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. Based on the validated models, followed by exploratory sensitivity studies, detailed parametric assessments are carried out. The parameter ranges are selected to cover historical masonry materials, consisting of bricks and mortar, and address both dry and wet conditions. Four typical failure modes, namely, flexural strut crushing, diagonal cracking, flexural toe crushing, and mixed sliding, in an order of increasing ductility, are quantified and discussed. It is shown that wet masonry walls have an average reduction of 16% in terms of stiffness and capacity compared with the dry counterparts. Although the failure modes in dry and wet wall pairs are similar, some cases are identified in which the weaker moisture-affected joint strength results in a shift to a more brittle mode. It is also shown that the ductility of the flexural strut crushing mode, which often governs the failure of historical masonry due to its low strength, is considerably overestimated in existing guidelines. Based on the results of the parametric investigations, analytical models for predicting the inelastic response are evaluated, and suggestions for modifications are proposed.

M Elzeadani, D V Bompa, A Y Elghazouli (2022)One Part Alkali Activated Materials: A State-of-the-Art Review, In: Journal of Building Engineering57104871

This article assesses the state-of-the-art for research on one-part alkali-activated materials, with particular emphasis on recent work dealing with the constituent materials, preparation methods, fresh properties, mechanical properties, and durability characteristics. The review, which covers over 170 studies, first discusses the different precursors, solid activators, admixtures, and aggregates used within such materials. Preparation techniques of one-part alkali-activated materials are then addressed, including pre-mixing treatment, mixing and curing, and 3D-printing. Reaction mechanisms and resulting binding phases are also outlined, followed by a detailed discussion on the fresh, mechanical and durability characteristics. The sensitivity of the compressive strength to different precursors and solid activators with varying chemical compositions, is examined, and predictive strength equations are proposed for common mixes. A brief comparison between the fresh, mechanical and durability characteristics of one-part and two-part AAMs is outlined, followed by a discussion on design standards as well as health and environmental aspects. The review concludes with suggestions for future research for key applications, with due consideration to the projected availability of precursors and the sustainability of solid activators. It is shown that despite the significant recent developments on one-part alkali-activated materials, further progress necessitates future research with a focus on optimising mixes made from precursors other than fly ash and blast furnace slag, as well as detailed investigations on structural members and components.

Dan Bompa, A.Y. Elghazouli (2019)Behaviour of confined rubberised concrete members under combined loading conditions, In: Magazine of Concrete Researchpp. 1-55 ICE Publishing

This paper presents an experimental study into the fundamental response of reinforced concrete members, which incorporate rubber particles obtained from recycled tyres, subjected to combined axial–bending loading conditions. Tests on confined circular members with and without internal hoops or external fibre-reinforced polymer (FRP) sheets are described. The results show that the rubber particles enhance the confinement level activated, with confined/unconfined strength and deformation capacity ratios at least twice those of conventional concrete members. The hoop-confined members provided with 30% rubber developed a typical reinforced concrete behaviour, with relatively limited deformation capacity in comparison with FRP-confined members. The external confinement substantially enhanced the ultimate rotation of members incorporating 30% rubber, with ductility factors reaching up to ten for relatively small eccentricity levels. An increase in rubber content to 60% had a detrimental effect on the axial capacity, but increased the ultimate rotation up to twice in comparison with members with 30% rubber. Based on the test results, a design-oriented constitutive model for FRP-confined concrete and a variable confinement procedure for assessing the strength interaction of circular sections are proposed. The suggested procedures capture, in a realistic manner, the influence of rubber content on the strength and deformation characteristics of confined members.

A Y Elghazouli, D V Bompa, S A Mourad, A Elyamani (2021)In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions, In: Bulletin of earthquake engineering SPRINGER

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

D.V Bompa, A.Y Elghazouli (2021)Mechanical properties of hydraulic lime mortars and fired clay bricks subjected to dry-wet cycles, In: Construction and Building Materials303124458 Elsevier

This paper examines the influence of moisture and chlorides on the mechanical properties of natural hydraulic lime mortars, fired clay brick materials and masonry components. Besides assessing three types of mortars incorporating limes with different hydraulicity levels, a cement-only mortar was also investigated for comparison purposes. The test results indicate that all the hydraulic lime mortars had mass accumulation in the range of 11–14% after being subjected to wet-dry cycles in a sodium chloride solution, whilst the mass uptake was in the range of 3–8% for those made of cement. Salt accumulation produced a denser material leading to compressive cube and flexural strength enhancements by factors ranging between 1.6 and 4.7 in comparison to those in ambient-dry conditions, with even higher factors obtained for compressive cylinder strengths and elastic moduli. In contrast, lime mortar subjected to water-only wet-dry cycles showed constant mass or mass loss, due to cracking. Uniaxial compressive strengths of cylindrical brick cores were about 8.5% higher due to wet-dry cycles in chloride solution, and by about 14.9% lower due to wet-dry cycles in water, compared to the ambient-dry case. Complementary compressive tests on masonry cylinders in ambient-dry conditions were also used to assess the adequacy of existing compressive strength assessment expressions. After modifying the expressions by a set of proposed calibration factors, these are employed to undertake a sensitivity study using the mechanical properties of mortars and bricks subjected to wet-dry cycling. The results of the sensitivity study, combined with strength ranges available in the literature, lead to an identification of a suitable range of materials that can be considered for rehabilitation of some forms of historic masonry.

D.V Bompa, A. Y. Elghazouli (2020)Compressive behaviour of fired-clay brick and lime mortar masonry components in dry and wet conditions, In: Materials and Structures53(3) Springer

This paper examines the fundamentalmechanical properties of masonry elements incorpo-rating fired-clay bricks and hydraulic lime mortarsunder ambient-dry and wet conditions, correspondingto 48 h submersion in water. In addition to comple-mentary material characterisation assessments, twotypes of specimens are tested: cylindrical cores incompression, and wall elements in compression.Overall, a detailed account of more than 50 tests isgiven. Apart from conventional measurements, the useof digital image correlation techniques enables adetailed assessment of the influence of moisture on theconstitutive response, confinement effects andmechanical properties of masonry components. Theuniaxial compressive strengths of wet brick elementsand brick–mortar components, resulting from tests oncylindrical cores with height-to-depth ratios of aroundtwo, are shown to be 13–18% lower than those inambient-dry conditions. The tests also show thatenhanced confinement levels in brick units mobilise67–92% higher strengths than in the correspondingunconfined cylinders. Moreover, experimental obser-vations indicate that the presence of significantconfinement reduces the influence of moisture on themechanical properties as a function of the brick andmortar joint thickness and their relative stiffness. As aresult, the failure of wet masonry walls in compressionis found to be only marginally lower than those inambient-dry conditions. Based on the test results, theinfluence of moisture on the constitutive response andmechanical properties of masonry components isdiscussed, and considerations for practical applicationare highlighted

A Mujdeci, D. V. Bompa, A.Y. Elghazouli (2021)Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading, In: Archives of Civil and Mechanical Engineering2153 Springer

This paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

Ayse Mujdeci, Dan Bompa, Ahmed Elghazouli (2021)Structural performance of composite steel rubberised concrete members under combined loading conditions, In: ce/papers4(2-4)pp. 641-647

This paper investigates the structural behaviour of rubberised concrete-filled steel tubular (RuCFST) members under a wide range of axial-bending loading conditions. The results of an experimental programme on circular concrete-filled steel tubes (CFST), incorporating conventional and rubberised concrete (RuC) materials with various rubber content ratios, are presented. After describing the specimen details and testing arrangements, the influence of the RuC infill on the behaviour of test members in terms of moment-axial interaction and ductility, is examined. The test results show that whilst the cross-sectional capacity of RuCFST members is reduced with the increase in rubber content, significantly higher ductility is obtained compared with conventional counterparts. An enhancement of about 85% in ductility is obtained for members with 60% rubber content compared to those with conventional concrete. Finally, the test results are compared with current design guidelines, indicating that the latter tend to overestimate the capacity, particularly for relatively high rubber contents.

This paper investigates the in-plane response of ambient-dry and wet clay-brick/lime-mortar masonry walls under lateral cyclic loading and co-existing compressive gravity load, as well as of square masonry panels under diagonal compression. The properties of the constituent materials were selected to resemble those of existing heritage masonry structures in Historic Cairo. After describing the specimen details and testing arrangements, the main results and observations are provided and discussed. The full load-deformation behaviour of the large-scale wall members is also evaluated , including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a detrimental effect on the main material properties, including the diagonal tension and compression strengths as well as brick-mortar interaction parameters. For the large-scale wall specimens, the wet-to-dry reduction was found to between 8-11% for the lateral strength and around 10% in terms of ductility. The response of diagonal walls was relatively brittle with a reduction between wet-to-dry strengths of around 33%, suggesting that the reduction ratio is dependent on the compression stress level. Provided that the key moisture-dependent masonry properties are appropriately evaluated, it is also shown that analytical assessment methods can be reliably adapted for predicting the response.

Ofelia Corbu, Dan V Bompa, Henriette Szilagyi (2021)Eco-efficient cementitious composites with large amounts of waste glass and plastic, In: Proceedings of the Institution of Civil Engineers. Engineering sustainability174(2)pp. 1-11 ICE Publishing

This paper presents an experimental study, which has been lacking to date, into the properties and applications of Waste Glass-Plastic Cementitious (WGPC) composites incorporating recycled aggregates as a full replacement of natural aggregates, with direct application in highly eco-efficient construction components. Detailed experimental assessments on the fresh properties, strength, and durability characteristics of such composites are undertaken. Particular focus is given to the mix rationale and optimisation process as well as possible routes of exploitation of such materials in construction elements. Experimental assessments showed that such composite materials meet the strength and durability criteria for direct application in practice. The best balance in terms of strength and workability was achieved for a waste glass-to-plastic aggregate ratio of 92/8. The presence of relatively large amounts of recycled waste glass particles with small sizes acted as secondary hydration products and contributed to achieving an adequate strength of the material. Besides lower unit weight and superior thermal properties compared to conventional concrete, WGPC components have shown a reliable behaviour under vehicle impact loading and potential wider application in sustainable non-structural construction applications.

This paper examines the performance of multi-binder conventional geopolymer mixes (GCMs) with relatively high early strength, achieved through curing at ambient temperature. Mixes incorporating ground granulated blast-furnace slag (GGBS), fly ash (FA) and microsilica (MS) and sodium metasilicate anhydrous, were assessed in terms of workability, mechanical properties and embodied carbon. A cement mortar was also prepared for the sake of comparison. The best performing GCM was then used as a reference for rubberised geopolymer mixes (RuGM) in which the mineral aggregates were replaced by recycled rubber particles in proportions up to 30% by volume. Experimental results were combined with embodied carbon estimations in a multi-criteria assessment to evaluate the performance of each material. A mix with a 75/25 GGBS-to-FA ratio, in which 5% MS was added, had the best performance in terms of strength, workability, water absorption and environmental impact. The compressive strength was above 50 MPa, similar to that of the cement mortar. The latter had significantly higher embodied carbon, with factors ranging between 3.48 to 4.20, compared with the CGM mixes. The presence of rubber particles reduced the mechanical properties of RuGM proportionally with the rubber amount, but had similar workability and embodied carbon to CGMs. Finally, a strength degradation model is validated against the tests from this paper and literature to estimate the compressive strength of RuGM, providing reliable predictions over a wide range of rubber contents.

M Elzeadani, D. V. Bompa, A Y Elghazouli (2021)Preparation and properties of rubberised geopolymer concrete: A review, In: Construction and Building Materials313125504 Elsevier

Interest in geopolymer concrete (GeoPC) and in rubberised concrete (RuC) has grown over the past two decades. The former offers an attractive alternative to ordinary Portland cement (OPC) concrete given its environmental footprint, while the latter provides a sustainable solution to tyre recycling and helps mitigate the depletion of natural aggregates. The benefits of combining the merits of GeoPC and RuC to form rubberised geopolymer concrete (RuG) as a potential sustainable construction material have been recognised in the past few years. As such, this paper presents a detailed review of RuG highlighting its constituent components, preparation and curing aspects, fresh and physical qualities, durability features, and thermal and sound insulation qualities, with a particular focus on mechanical properties. The influence of crumb rubber replacement on key characteristics is critically reviewed, including the effect of binder type, alkaline solution, alkaline solution-to-binder content, and curing conditions. Comparative quantitative assessments and prediction relationships are also presented where relevant. Finally, gaps in the available literature and recommendations for future research are outlined, with a view to supporting further developments in research and future deployment of RuG materials in practice. Whilst previous studies demonstrate the significant potential of RuG and provide essential information on its fundamental properties, this review reveals that much research is still needed in order to optimise the merits of the material and to provide a full characterisation of its behaviour at both the material and structural levels under various loading conditions.

M I Moharram, D. V. Bompa, B Xu, A Y Elghazouli (2022)Behaviour and design of hybrid RC beam-to-steel column connections, In: Engineering Structures250113502 Elsevier

This paper deals with the performance and design of hybrid connections between steel columns and RC beams by means of shear-keys, through detailed nonlinear numerical assessments in which the influence of key geometric and material parameters on the ultimate behaviour is examined. The numerical simulations employ concrete damage plasticity modelling and procedures which are validated against test results on hybrid members. Extensive parametric assessments involving over two hundred three-dimensional models are carried out, with focus on the effects of varying the shear-key embedment length and section size, longitudinal and transverse reinforcement ratios, concrete strength, and cross-section size. The numerical results enable an in-depth understanding of the main mechanisms governing the ultimate response which can occur in shear, flexure, crushing of a direct strut at the steel-to-concrete interface, or yielding of the shear-key at the column face. Based on the findings from the numerical assessments coupled with test observations, procedures and expressions are proposed for the design of critical regions and of the shear-key. The suggested design expressions are shown to provide reliable predictions across a wide range of shear-key length-to-depth ratios, thus offering a simple method suitable for the application of hybrid connections with shear-keys in design practice.

Marian Sabău, DAN BOMPA, Luis F. O. Silva (2021)Comparative carbon emission assessments of recycled and natural aggregate concrete: Environmental influence of cement content, In: Geoscience Frontiers12(6)101235 Elsevier B.V

This work examines the environmental and geochemical impact of recycled aggregate concrete production with properties representative for structural applications. The environmental influence of cement content, aggregate production, transportation, and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region. To obtain a detailed insight into the optimum life cycle parameters, a sensitivity study is carried out in which supplementary cementitious materials, different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered. The results show that carbon emissions were between 323 and 332 kgCO2e per cubic metre of cement only natural aggregate concrete. These values can be reduced by up to 17% by replacing 25% of the cement with fly ash. By contrast, carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50% and 100%, and transportation is not included in analysis. However, the concrete with 50% recycled aggregate presented lower increase, only 0.3% and 3.4% for normal and high strength concrete, respectively. In some cases, the relative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%, and case-specific transportation distances were considered. In absolute values, the concrete mixes with 100% recycled aggregates and 25% fly ash had lower carbon emissions than concrete with cement and natural aggregates only. Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short (15–25 km) and the cement replacement by fly ash is equal or higher than 25%, considering that the mechanical properties are adequate for practical application. The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete, recommending them as an alternative to achieving global sustainability standards in construction.

C. Ţibea, Dan V. Bompa (2020)Ultimate shear response of ultra-high-performance steel fibre-reinforced concrete elements, In: Archives of Civil and Mechanical Engineering20(2) Elsevier

This paper examines the experimental performance of ultra-high-performance steel fibre-reinforced concrete (UHPSFRC) beams subjected to loads at relatively low shear span-to-depth ratios. The results and observations from six tests provide a detailed insight into the ultimate response including shear strength and failure mode of structural elements incorporating various fibre contents. The test results showed that a higher fibre content results in an increase in ultimate capacity and some enhancement in terms of ductility. Detailed nonlinear numerical validations and sensitivity studies were also undertaken in order to obtain further insights into the response of UHPSFRC beams, with particular focus on the influence of the shear span-to-depth ratio, fibre content and flexural reinforcement ratio. The parametric investigations showed that a reduction in shear span-to-depth ratio results in an increase in the member capacity, whilst a reduction in the flexural reinforcement ratio produces a lower ultimate capacity and a relatively more flexible response. The test results combined with those from numerical simulations enabled the development of a series of design expressions to estimate the shear strength of such members. Validations were performed against the results in this paper, as well as against a collated database from previous experimental studies.

B. Xu, D.V Bompa, A.Y. Elghazouli (2020)Cyclic stress–strain rate-dependent response of rubberised concrete, In: Construction and Building Materials254119253 Elsevier

This paper presents an experimental investigation into the constitutive response of rubberised concrete materials under monotonic and cyclic compression. After describing the test specimens and experimental arrangement, a detailed account of the stress–strain response of rubberised concrete materials, as well as their reference high strength conventional concrete, is given. The volumetric rubber content is varied between 0 and 40% of both fine and coarse aggregates. Both monotonic and cyclic loading conditions are considered for comparison, and three strain rate levels, simulating static, moderate and severe seismic action, are examined. The increase in rubber content is shown to have a detrimental effect on the stiffness and strength, as expected. However, with the increase in rubber content, rubberised concrete materials are shown to exhibit improved compressive recovery under cyclic loading, coupled with a higher energy accumulation rate, enhanced inter-cycle stability and lower inter-cycle degradation. It is also shown that the increase in strain rate, from static to severe seismic, leads to a notable increase in the stiffness and strength, with these enhancements becoming less significant with the increase in rubber content. Based on the results and observations, expressions for determining the unloading stiffness and residual strain, as a function of rubber content and strain rate, are proposed within the ranges considered. The suggested relationships enable the characterisation of rubberised concrete materials within widely used cyclic constitutive models.

B. Xu, D.V Bompa, A.Y. Elghazouli, A.M. Ruiz-Teran, P.J. Stafford (2019)Numerical assessment of reinforced concrete members incorporating recycled rubber materials, In: Engineering Structures204110017 Elsevier

This paper is concerned with the inelastic behaviour of reinforced concrete beam-column members incorporating rubber from recycled tyres. Detailed three-dimensional nonlinear numerical simulations and parametric assessments are carried out using finite element analysis in conjunction with concrete damage plasticity models. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from a series of tests involving conventional and rubberised concrete flexural members and varying levels of axial load. The influence of key parameters, such as the concrete strength, rubber content, reinforcement ratio and level of axial load, on the performance of such members, is then examined in detail. Based on the results, analytical models are proposed for predicting the strength interaction as well as the ductility characteristics of rubberised reinforced concrete members. The findings permit the development of design expressions for determining the ultimate rotation capacity of members, using a rotation ductility parameter, or through a suggested plastic hinge assessment procedure. The proposed expressions are shown to offer reliable estimates of strength and ductility of reinforced rubberised concrete members, which are suitable for practical application and implementation in codified guidance.

Bowen Xu, Hui Li, DAN BOMPA, Ahmed Y. Elghazouli, Jiangbo Chen (2021)Performance of Polymer Cementitious Coatings for High-Voltage Electrical Infrastructure, In: Infrastructures6(9)125

This paper investigates the electrical, thermal and mechanical properties as well as the environmental performance of polymer cementitious composites (PCCs) as sustainable coating materials for underground power cables and as high-voltage insulators. Particular focus is placed on the optimised mix design and the effect of the manufacturing method on the performance of PCCs, incorporating liquid styrene and acrylic (SA) monomers, wollastonite and muscovite. Microstructural investigations, together with results from strength tests, indicate that the manufacturing method is a key performance parameter. Experimental results show that PCC mixes containing 25% SA emulsion, 12.5% wollastonite and no muscovite provide the most favourable dielectric properties from the mixes investigated. The PCC material has a dielectric strength up to 16.5 kV/mm and a dielectric loss factor lower than 0.12. Additional experiments also show that PCC has good thermal stability and thermal conductivity. The mechanical strength tests indicate that PCC specimens possess reliable strengths which are applicable in structural design. Environmental assessments also show that PCCs possess significantly lower embodied energy and embodied carbon than conventional plastic insulating materials

D.V Bompa, A.Y. Elghazouli (2019)Stress–strain response and practical design expressions for FRP-confined recycled tyre rubber concrete, In: Construction and Building Materials237117633 Elsevier

This paper presents an experimental programme on the response of fibre reinforced polymer (FRP) confined circular rubberised concrete (RuC) members in compression. After describing the constituent materials and testing arrangement, a detailed account of the complete stress–strain response of FRP-confined high strength conventional concrete materials (CCM) and RuC in uniaxial compression is provided. The parameters directly investigated through experimental assessment are the rubber content, namely 30% and 60% by volume of both fine and coarse aggregates, and the number of confinement layers which varies from 0 to 4. Experimental observations indicate that the confined compressive strength typically increases in a largely proportional manner with the unconfined compressive strength, whilst the confined axial strain at ultimate tends to increase with the rubber content. Confined-to-unconfined strength ratios above 9 and confined ultimate strain-to-unconfined crushing strain ratios above 40, are obtained for concrete with 60% rubber and four layers of confinement. These values are higher by factors of about 3.2 and 4.5 in comparison to the conventional reference concrete, respectively. The test results and observations enable the development of a series of design expressions to estimate the stress–strain response of circular RuC specimens passively confined with FRP sheets, with due account for the influence of rubber content. Validations performed against the material tests carried out in this paper, as well as those from previous studies on RuC and CCM with FRP confinement, indicate that the proposed expressions offer reliable predictions of the mechanical properties of FRP-confined members.

D.V Bompa, B Xu, A.Y Elghazouli (2021)Constitutive modelling and mechanical properties of cementitious composites incorporating recycled vinyl banner plastics, In: Construction & Building Materials275122159 Elsevier Ltd

This paper describes an experimental study, which has been lacking to date, into the mechanical properties of cementitious composites incorporating granules and fibres from recycled Reinforced PVC (RPVC) banners. A detailed account of over 140 tests on cylindrical, cubic and prismatic samples tested in compression and flexure, with up to 20% replacement of mineral aggregates, is given. Based on the test results, the uniaxial properties of selected recycled materials are examined in conjunction with a detailed characterisation of the RPVC granule size and geometry. Experimental measurements using digital image correlation techniques enable a detailed interpretation of the full constitutive response in terms of compression stress-strain behaviour and flexural stress-crack opening curves, as well as key mechanical parameters such as strength, elastic modulus and fracture energy. It is shown that the mechanical properties decrease proportionally with the amount of RPVC. For each 10% increment of volumetric replacement of mineral aggregates, the compressive strength is halved whilst the flexural strength is reduced by about 30% compared to their conventional counterparts. The reduction in strength is counterbalanced by an improved ductility represented by a favourable post-peak response in compression and an enhanced flexural softening and post-cracking performance. Smaller particles, with a relatively long acicular or triangular geometry, exhibited better behaviour as these acted as fibres with improved bond properties in comparison with intermediate and large size granules. The test results and observations enable the definition of a series of expressions to determine the mechanical properties of cementitious materials incorporating RPVC and other waste plastics. These expressions are then used as a basis for an analytical model for assessing the compressive and tensile stress-strain response of such materials. Validations carried out against the tests undertaken in this study, as well as from previous investigations, indicate that the proposed expressions and the developed constitutive model offer reliable representations for practical application.

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