Comparative carbon emission assessments of recycled and natural aggregate concrete: Environmental influence of cement content

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

Failure analysis of edge flat-slab column connections with shear reinforcement

Flat-slab column connections are susceptible to brittle failure, which lead to the necessity of improving ductility and ultimate strength. In case of edge connections, the behaviour at ultimate state is highly influenced by nonsymmetrical distribution of stresses originated by a moment transfer between the slab and the column. The paper presents the test results of three full-scale reinforced concrete flat-slab edge connections with stud-rail shear reinforcement subjected to concentrated load. The in plane dimensions of the slabs are constant, 2200 mm x 2000 mm, whereas the slab thickness varies from 200 mm to 260 mm. A comprehensive analysis is made regarding the behaviour at failure by means of analytical studies and a number of comparisons to code provisions

Eco-efficient cementitious composites with large amounts of waste glass and plastic

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

Structural response of hybrid timber ‐ cold formed steel floors

The paper examines the composite performance of hybrid steel-timber lightweight floor assemblies incorporating cold-formed steel (CFS) profiles and plywood (PW) flooring panels with varying degrees of shear connection achieved by means of self-drilling screws. Material, push-out, and three-point short-span floor tests with or without web openings were carried out. The results and observations from the tests provide a detailed insight into the inelastic properties and ultimate response of such floor systems. Push-out tests indicate that denser connector arrangements increase connection stiffness, while push-out and short beam tests suggest an optimum connector spacing equal to the beam depth for a balance between structural performance and constructability. The experimental observations indicate that the ultimate condition of the short composite beams was characterized by CFS web crippling under the load application point, followed by a pull-through of the self-drilling screws. Web openings reduced the strength of the floor elements compared to the members with full webs. Complementary numerical studies are undertaken using nonlinear finite element procedures which were validated against the beam tests, offering a detailed insight into the stress levels in the timber, steel, and connectors. Codified procedures for determining the capacity of composite CFS sections are compared with the test results, and guidance for the practical design and construction of such systems is given

Preparation and performance of sugarcane bagasse ash pavement repair mortars

Pavement rehabilitation is typically required to ensure the service life of the road and the safety of road traffic. Due to various environmental and loading factors, pavements can present degradation or failures along their length, such as cracks, fissures, deformations, and disintegration of the wearing course. One way to reapair these defects is by using sealant materials. The objective of this research is to design mortars with sugarcane bagasse ash as a substitute for sand for the repair of cracks in pavements. Compression, tensile, shrinkage, fluidity and adherence tests were carried out on mortar samples that varied their dosage with 0 %, 50 % and 75 % ash content as a substitute for sand. These tests allowed for the evaluation of the physical and mechanical properties of the samples, determining compressive strength values of 16.65 MPa, adhesion of 0.52 MPa, among others. The control mix 5 with a 50 % replacement of ash by sand (M5–50 %), obtained the best results under the criteria of each of the tests performed. This article also evaluates the environmental impact of construction materials using the established procedures, finding that considering sugarcane bagasse ash as waste, using recycled polypropylene fibers, and incorporating zeolite for carbon capture can reduce the carbon footprint of concrete by up to 50 % compared to baseline mixes

Behavior of unreinforced multi-leaf stone masonry walls under axial compression: Experimental and numerical investigation

This paper presents an experimental and numerical investigation on the behavior and failure mechanisms of unreinforced multi-leaf masonry walls. The main objective of this study is to explore the propagation of cracking, ultimate load, and deformation characteristics of different typologies of three-leaf walls commonly found in historic masonry. Axial compression tests on scaled three-leaf wallettes built of limestone units and lime-based mortar, as well as experiments on constituent materials for each leaf, were carried out. The main results obtained from the experimental tests are the mechanical characteristics, stress–strain curves, stress distributions in multileaf masonry walls. The research findings elucidate a strong correlation between the bearing capacity of multileaf walls and the thickness ratio of the inner-core layer to the external layers. This relationship underscores the critical significance of the inner-core layer in efficiently carrying the applied vertical loads. Furthermore, the extent to which the inner-core layer actively contributes to load-bearing is contingent upon the interconnectivity among the three layers. Walls with keyed collar joints have a higher strength and stiffness than the walls without transverse tying, with the strength being comparatively higher by about 9–13 %. This clarifies the contribution of the inner core layer and that of the two outer layers in resisting vertical loads and enhancing the overall composite behavior of the wall. Finally, these results allow for validating non-linear numerical procedures based on two-dimensional plane strain modelling along wall thickness and a simplified micro-modelling approach, which prove to be adequate tools for detailed modelling of masonry components of similar nature

Dynamic Characterisation of a Heritage Structure with Limited Accessibility Using Ambient Vibrations

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