Impact resistance of deflection-hardening fiber reinforced concretes with different mixture parameters

YesThe impact behavior of deflection-hardening High Performance Fiber Reinforced Cementitious Concretes (HPFRCs) was evaluated herein. During the preparation of HPFRCs, fiber type and amount, fly ash to Portland cement ratio and aggregate to binder ratio were taken into consideration. HPFRC beams were tested for impact resistance using free-fall drop-weight test. Acceleration, displacement and impact load vs. time graphs were constructed and their relationship to the proposed mixture parameters were evaluated. The paper also aims to present and verify a nonlinear finite element analysis, employing the incremental nonlinear dynamic analysis, concrete damage plasticity model and contact surface between the dropped hammer and test specimen available in ABAQUS. The proposed modelling provides extensive and accurate data on structural behavior, including acceleration, displacement profiles and residual displacement results. Experimental results which are further confirmed by numerical studies show that impact resistance of HPFRC mixtures can be significantly improved by a proper mixture proportioning. In the presence of high amounts of coarse aggregates, fly ash and increased volume of hybrid fibers, impact resistance of fiberless reference specimens can be modified in a way to exhibit relatively smaller displacement results after impact loading without risking the basic mechanical properties and deflection-hardening response with multiple cracking

Mechanical and microstructural characterization of geopolymers from assorted construction and demolition waste-based masonry and glass

YesGeopolymers are mostly produced with main-stream precursors such as fly ash and slag. These precursors are successfully used and competitively demanded by the cement industry. Development of geopolymers from alternative precursors is appealing. The main aim of this work is the development of geopolymers with construction and demolition waste-based precursors including masonry units (red clay brick, roof tile, hollow brick) and glass. Different curing temperatures (50, 65, 75, 85, 95, 105, 115, 125 oC), curing periods (24, 48, 72 h), and Na concentrations (10, 12, 15%) of alkaline activator (NaOH) were employed. Compressive strength testing and microstructural investigations were performed including X-ray diffraction, thermogravimetry and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Results showed that depending on the type of precursor (hollow brick), curing temperature/period (115 oC/24 h) and concentration of alkaline activator (12%), it is possible to obtain compressive strength results more than 45 MPa. Hollow brick is the most successful precursor resulting in higher compressive strength results thanks to a more compact microstructure. The strength performance of red clay brick and roof tile is similar. The compressive strength results of geopolymers with glass precursor are lower, most probably due to significantly coarser particles of glass used. The main reaction products of red clay brick-, roof tile- and hollow brick-based geopolymers are sodium aluminosilicate hydrate (N-A-S-H) gels with zeolite-like structures while they are sodium silicate gels in the case of glass-based geopolymers. Our findings showed that CDW-based materials can be used successfully in producing geopolymers. Current research is believed to help raise awareness in novel routes for the effective utilization of such wastes which are realistically troublesome and attract further research on the utilization of CDW-based materials in geopolymer production.The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council (TUBITAK) of Turkey and British Council provided under projects: 117M447 and 218M102

Mechanical properties of cotton fabric reinforced geopolymer composites at 200-1000 °C

Geopolymer composites containing woven cotton fabric (0–8.3 wt%) were fabricated using the hand lay-up technique, and were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. With an increase in temperature, the geopolymer composites exhibited a reduction in compressive strength, flexural strength and fracture toughness. When heated above 600 °C, the composites exhibited a significant reduction in mechanical properties. They also exhibited brittle behavior due to severe degradation of cotton fibres and the creation of additional porosity in the composites. Microstructural images verified the existence of voids and small channels in the composites due to fibre degradation

Electrical testing for the assessment of self-healing and self-sensing capability of cementitious composites

Engineered Cementitious Composites (ECC) is regarded as a multifunctional smart material due to its intrinsic autogenous self-healing and self-sensing attributes. Here, recent findings related to the utilization of electrical measurements in analyzing combined effectiveness of autogenous self-healing and self-sensing attributes in ECC are discussed. It is concluded that electrical testing which are already widely used for self-sensing, can also be used successfully in estimating the autogenous self-healing efficiency in ECC. It is believed that further research into developing/understanding methods to rapidly and accurately characterize the multifunctional properties of such smart materials will significantly fasten their development and wider practical adoption. © 2019, Associated Cement Companies Ltd.. All rights reserved.National Council for Scientific ResearchThe authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council (TUBITAK) o

Performance of engineered cementitious composites under drop-weight impact: Effect of different mixture parameters

Current research focuses on the experimental and numerical determination of impact performance of engineered cementitious composites (ECC). Performance assessment of ECC beams with different mixture parameters was made. Mixtures were produced with different replacement rates of Class-F fly ash and slag with Portland cement, water to binder ratios and fiber types (polyvinyl alcohol [PVA] and nylon [N]). Experimental works were validated with incremental dynamic analyses performed by ABAQUS finite element software. Impact testing results were further supported by mechanical property results. Results reveal that each individual mixture parameter used is distinctively effective in modifying the properties under both sudden impact and slow static loading. In brief, enhanced impact resistance is noted when ECC is produced with slag, low amounts of pozzolanic materials, low W/B ratio, fiber addition and PVA fibers. Experimental results were also in line with the numerical results from ABAQUS largely. Significantly, cost-effective N fibers were also shown to be fully replaceable with costly PVA fibers without jeopardizing mechanical/impact performance, if mixture design parameters are adjusted suitably. Current research is likely to attract further research on the development of ECC that is with lower cost and comparable impact/mechanical performance with regards to widely studied more expensive counterparts in the literature. © 2019 fib. International Federation for Structural Concret

Mechanical and microstructural characterization of geopolymers from assorted construction and demolition waste-based masonry and glass

Geopolymers are mostly produced with main-stream precursors such as fly ash and slag. These precursors are successfully used and competitively demanded by the cement industry. Development of geopolymers from alternative precursors is appealing. The main aim of this work is the development of geopolymers with construction and demolition waste-based precursors including masonry units (red clay brick, roof tile, hollow brick) and glass. Different curing temperatures (50, 65, 75, 85, 95, 105, 115, 125 °C), curing periods (24, 48, 72 h), and Na concentrations (10, 12, 15%) of alkaline activator (NaOH) were employed. Compressive strength testing and microstructural investigations were performed including X-ray diffraction, thermogravimetry and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Results showed that depending on the type of precursor (hollow brick), curing temperature/period (115 °C/24 h) and concentration of alkaline activator (12%), it is possible to obtain compressive strength results more than 45 MPa. Hollow brick is the most successful precursor resulting in higher compressive strength results thanks to a more compact microstructure. The strength performance of red clay brick and roof tile is similar. The compressive strength results of geopolymers with glass precursor are lower, most probably due to significantly coarser particles of glass used. The main reaction products of red clay brick-, roof tile- and hollow brick-based geopolymers are sodium aluminosilicate hydrate (N-A-S-H) gels with zeolite-like structures while they are sodium silicate gels in the case of glass-based geopolymers. Our findings showed that CDW-based materials can be used successfully in producing geopolymers. Current research is believed to help raise awareness in novel routes for the effective utilization of such wastes which are realistically troublesome and attract further research on the utilization of CDW-based materials in geopolymer production. © 2020 Elsevier Ltd117M447, 218M102The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council (TUBITAK) of Turkey and British Council provided under projects: 117M447 and 218M102