In this study, it was aimed to produce the multifunctional cementitious composites with advanced thermal and electrical performance considering that these composites having high conductivity serve for the purpose of de-icing, electromagnetic shielding, anti-static, anti-corrosion, and so on. Carbon fiber (CF), and carbon powder (CP) were used singly or together to develop cementitious composites having high conductivity. The electrical resistance and thermal conductivity tests were performed to measure the conductivity of the cementitious composites. While mini-spreading test was applied to assess the consistency of the fresh-state cementitious composites containing conductive materials, in order to determine the distribution of the conductive material incorporated, SEM images were analyzed. In addition, compressive strength tests were carried out to determine the mechanical properties. According to the test results, the highest electrical conductivity result (197 Ω on the 1st day) were obtained from the binary mixtures, while the highest thermal conductivity result (1250 mW/m.K on the 7st day) were obtained from the mixtures containing only CP (by volume %0.6). 0.5% carbon fiber by volume mixture performed the worst in terms of mechanical and workability, with 20.5 MPa lower compressive strength and 16 cm lower mini-spread diameter values when compared to the control mixture.

The present investigation has been designed to assess the performance of pervious concrete prepared with Fly Ash (FA) and Recycled Concrete Aggregates (RCA) in place of Portland Cement (PC) and Natural Aggregates (NA). The percentage of NA replacement with RCA was in the proportion of 0%, 50%, and 100%, while the percentage of FA substitution was fixed at 10%. Various fresh (workability and consistency), mechanical (compressive strength, split tensile, and shear strength), durability (abrasion resistance, freeze thaw, flexure, and acid resistance), and microstructural (SEM and EDS) properties of pervious concrete have been evaluated at different curing periods. The findings reveal that the incorporation of RCA at different levels and partial substitution of FA proves to be desirable for the use of pervious concrete for structural and pavement construction purposes. Furthermore, incorporation of 10% FA in addition to higher levels of RCA proves significantly beneficial in refining the microstructural behaviour of pervious concrete. A homogenous micrograph with dense and layered C-S-H and C-H with was observed for mix made with 10% FA and 100% RCA.

The objective of this study is to develop a simplified numerical model that can be used to accurately and quickly conduct the collapse analysis of reinforced concrete (RC) frames impacted by vehicle in 45-degree oblique direction. The simplified numerical model included introduce of a simplified RC frame and a simplified vehicle. For the simplified RC frame, a mixed modeling technique was used in which structural components that experienced serious damage were simulated using detailed elements, while the retained structural components were simulated by macro elements. A constraint algorithm of nodal rigid body in LS-DYNA was adopted to guarantee the displacement compatibility of two kinds of element. For the simplified vehicle model, the spring-mass system was improved on the basis of the energy conservation principle to represent the vehicle in a 45-degree oblique impact. Combining the simplified RC frame model and vehicle model, the impact response of RC frame subjected to vehicle impact was studied and compared with the results of detailed RC frame model impacted by detailed vehicle. The validation confirmed that these introduced simplifications could significantly improve the computational efficiency and ensure the computational accuracy for the collapse analysis of RC frame subjected to vehicle impact.

Silicomanganese slag (SS) is a byproduct of the ferroalloy industry and cause environmental pollution and consume resources. In this study, the authors explored the use of water glass immersion to improve the performance of SS and used it to produce ultra-high performance concrete (UHPC). The results showed that SS treating with a 2% water glass concentration for 24 hours resulted 16 MPa higher compressive strength for composite than pure UHPC. Additionally, the treated composite had approximately half the mass and compressive strength losses of pure UHPC after freeze-thaw test, indicating that the treatment had a significant positive effect on the freeze-thaw resistance of ultra-high silicomanganese slag performance concrete (UHPSSC). Micro-structural analysis also showed that water glass immersion optimized the morphology of UHPSSC, contributing to improved mechanical performance and freeze-thaw resistance of the composite.

The precast N-system based on embedded-pin connections is used widely for constructing large precast industrial halls in south-eastern Europe and further afield, including areas of high seismicity. To assess realistically the seismic performances, safety margins and limitations of the connections, experimental investigations are essential. Experimental results from laboratory tests on a large-scale prototype model of the original roof beam–column connection show its actual bearing capacity, damage propagation pattern and specific failure mode. The experimental study was then extended to a prototype model of an upgraded roof beam–column connection. For better safety, the connection was upgraded with improved concrete confinement and stronger steel connecting pins. The experimental results show clearly that the implemented method for upgrading the pin-based connection provided very limited upgrading effects. To obtain much better and more reliable safety upgrading, a new innovative and effective upgrading method had to be developed. The capability of the implemented refined nonlinear three-dimensional micro-modelling concept to simulate realistically the complex nonlinear response of the tested original and upgraded roof beam–column connections was demonstrated by an extensive analytical simulation study.

The fundamental properties and durability of mortar mixed with phytoncide, zeolite or copper powder were evaluated. For different phytoncide substitution ratios (SRs), there was no significant difference in the flow, compressive strength and flexural strength of the mortar. With an increase in the SR of zeolite, the workability decreased, while the compressive strength, flexural strength and chloride penetration resistance increased. The compressive and flexural strengths of the mortars mixed with copper powder were higher than those of the reference mix. With an increase in the SR of copper powder, the flow slightly increased and the chloride penetration resistance decreased.

Fire spalling prediction of fibre-reinforced concrete containing polypropylene (PP) or steel fibre at elevated temperatures is challenging. It is difficult to use conventional methods, such as finite-element modelling and discrete-element modelling, to solve the problem, because of the complicate coupling mechanism of PP and steel fibres in concrete. To this end, two artificial neural network (ANN) models, one (ANN1) based on a concrete mix study and the other (ANN2) based on a compressive strength study, were introduced to assess the resistance of concrete to explosive spalling. Test data (321 and 318 items, respectively) gathered from the literature were utilised to train the proposed models. Twenty-four concrete mixes (96 groups), that is, seven plain concrete mixes, four high performance concrete mixes reinforced with PP fibre, three ultra-high-performance concrete (UHPC) mixes with reinforced PP fibre and ten UHPC mixes reinforced with PP and steel hybrid fibres were designed and tested to validate the accuracy of the models. The study demonstrates that ANN1 and ANN2 can achieve a predictive accuracy of 89.6% and 84.4% for the explosive spalling, respectively, indicating the feasibility of the proposed models for predicting explosive spalling threat of the hybrid fibre-reinforced concrete.

Construction and demolition waste (CDW) management and recycling practices are crucial for transitioning to a circular economy. The focus of this study was on the detailed characterisation of different CDWs (hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete and glass) collected from seven different demolition sites in Turkey. The CDWs were characterised based on particle size distribution, chemical composition and crystalline nature. Pozzolanic activity was evaluated through compressive strength measurements of cement mortars made with 20% cement replacement by CDWs at 7, 28 and 90 days. The results showed that the clayey CDWs exhibited similar physical/chemical properties and crystalline structures. The compositions of the waste concretes varied significantly based on their original materials. All the CDWs satisfied the minimum strength activity index (SAI) for supplementary cementitious materials, with pozzolanic activity influenced by the fineness and silica + alumina contents. The average SAIs for the HB, RCB, RT, concrete and glass were, respectively, 84.5%, 86.3%, 83.4%, 80.7% and 75.8%. Clayey CDWs contributed to mechanical strength development, while the contribution of concretes was related to the hydration of unreacted cementitious particles. Glass exhibited the weakest pozzolanic activity due to its coarser particle size. Overall, the CDWs demonstrated suitable properties for use as supplementary cementitious materials in Portland cement based systems.

Using geopolymer composites to replace Portland cement can decrease the carbon emission. This study focuses on improving the strength of geopolymer composite by reaching a positive hybrid effect between nano-calcium carbonate (NC) and polyethylene fiber (PF) of different lengths. Fresh and hardened properties, including flowability and strength, were employed to evaluate the hybrid effect. Generally, there was negative hybrid effects between PF with various length and NC in most of the examples on flowability, but the positive hybrid effects on strength. The combination of 12 mm +6 mm PF+1%NC obtains the highest hybrid effect on bending strength, resulting from the good fiber-matrix bond. The bending strength of PF reinforced geopolymer composite can be assessed based on a new regression coefficient A that takes into account of hybrid effect, fiber-matrix bond strength, and fiber dispersion. This new model of bending strength of PF-reinforced geopolymer composites developed in this paper is simpler and more effective than the old one in the literatures.

Evaluation of the damage and deformation of cast-in-situ concrete joints between the precast concrete track slabs of the China Railway Track System (CRTS) II is crucial to the safe operation of high-speed railways. To investigate the damage and deformation evolution of concrete joints under thermal action (caused by the natural meteorological environment) and vehicle loads, a two-dimensional thermal–mechanical coupled numerical model of concrete joints at the mesoscale was developed. This model analyses the influence of three factors – concrete strength, maximum diameter of the joint concrete aggregate and vehicle speed. First, meteorology and heat transfer theory were used in thermal simulations. Then, the non-linear characteristics of the joint concrete were modelled as a two-phase composite material based on the random aggregate algorithm and strain-based elastic damage theory at the mesoscale. The cohesive zone model was used to simulate the interfaces between precast slabs. The reliability of the proposed model was assessed using field measurements. The results of a numerical example showed that the maximum aggregate diameter of the joint concrete significantly affected damage evolution in the joint concrete and concrete strength has a slight effect on joint uplift.