Journal Feb 2022

Powder packing optimization for clinker reduction in concrete Mark Alexander, Matthew Holmes

Due to the vast quantities of concrete that are produced annually, the material represents substantial greenhouse gas (GHG) emissions, with clinker contributing the most significant portion. This paper presents an investigation aimed at reducing the clinker content required to achieve compressive strength while not detrimentally affecting workability, using particle packing modelling and limestone filler to replace clinker. The compaction interaction packing model (CIPM) and the modified Andreasen and Andersen curve (MAAC) were applied and integrated, the former for powder packing and the latter for fine and coarse aggregate packing. The CIPM was calibrated based on compaction effort applied experimentally, and predicted powder packing densities were validated experimentally. The integrated model was then applied to obtain optimized concrete mix designs with maximum packing density. Results showed that workability could be retained but compressive strength decreased relative to a reference mix. The binder efficiency index (kg binder/MPa/m3 concrete) showed very acceptable performance relative to the international literature, confirming that packing optimization was able to effect clinker reduction without detrimentally affecting compressive strength for strength classes < 50 MPa. There remains a need to maximize filler content in concrete mixtures and to better understand the fundamental influences of powder packing, to develop predictive processes that incorporate indicators of practical usability (such as water demand and expected workability) while maximising packing density.

Critical review on various aspects of geopolymer concrete Tanuja Gupta, Chakradhara Rao Meesala

This review paper presents the important outcomes of 144 research papers published in the open literature on geopolymer concrete (GPC), several fresh and hardened concrete, and hardened concrete properties have been dealt. Additionally, the development of strength of the GPC has been discussed with the help of microstructure study. The microstructure of the GPC in terms of durability against sulphate and acid attack has been reviewed. Also the structural performance of the GPC was discussed. Furthermore, the use of recycled concrete aggregate in geopolymer concrete has been discussed. Critical analysis of the results of the findings of different researchers in this paper may be useful for further research in this area.

Chemical characterization of cement composites- A FTIR study Maitri Mapa, T. Hemalatha

Chemistry of cement hydration is studied by many methods including spectroscopic method. Fourier transform infrared spectroscopy (FTIR) method works on the principle of absorption of infrared light at different wavelengths which are characteristics of chemical composition. Nowadays, in order to reduce the cement consumption in concrete, supplementary cementitious materials (SCMs) such as fly ash, ground granulated blast furnace slag (GGBS) are used as cement replacement materials. When such SCMs are used, hydration mechanism is altered that in turn affects the strength of cement concrete. For any improved properties of cement concrete, mixes need to be engineered or modified and is possible only when the hydration mechanism is properly understood. In view of this, in the present work, the hydration of fly ash / GGBS cement composites and engineered composites have been investigated by using the FTIR analysis. Modification in the major hydrates such as Portlandite and C-S-H are investigated. During the ageing of the hydrated cement paste, particularly, when pozzolanic material like fly ash is used, the polymerization of silica and the decalcification happens that are identified by the shift in the position of the major bands of C-S-H by the FTIR.

Effect of different modifications on physical and mechanical properties of EPS-cement based composite materials Youquan Liu, Qiaoxia An

Expanded polystyrene (EPS) - cement composite materials are characterized by light weight and good thermal insulation, in order to improve the physical and mechanical properties of EPS-cement composite materials. This paper studied the effect of modified EPS particles with different concentrations (1-10 %) of triethanolamine (TEOA) and silane coupling agent (SCA) on compressive strength, elastic modulus, thermal conductivity, and water absorption of EPS-cement composite material. It was found that adhesion between EPS particles and cementitious material paste effectively improved by modification. The compressive strength and elastic modulus of the composite could significantly be improved after the EPS particles modified by appropriate TEOA and SCA concentration. In particular, the early strength of the composite could be improved after the EPS particles modified by TEOA. Compared with the control, the compressive strength was increased by 57.32 % at the age of 3 days. The compressive strength of EPS-cement composite samples was increased by 22.2 and 21.14 % at 7and 28 days. Its modulus of elasticity was increased by 8 %. TEOA and SCA concentrations did not influence significantly water absorption and thermal conductivity of the EPS mixes. The thermal conductivity of the EPS specifications ranged from 0.21 to 0.32 w/(m·K), the cumulative water absorption after 24 hours of all mix specifications ranged from 11.27 to 13.24 %. In general, the modification effect of TEOA was better than that of SCA, and the recommended concentration of TEOA was 5-8 %.The study showed that EPS cement-based composites could have good thermal insulation properties and good mechanical properties after modification.

Effect of boric acid as set retarder on setting time and strength of geopolymeric binding materials Md Reyazur Rahman, Rakesh Paswan, S. K. Singh

Geopolymer is a potential alternative to ordinary Portland cementitious binder in terms of energy conservation and environment protection. However, utilization of geopolymer material is limited, due to practical difficulties such as rapid setting and poor workability. Therefore, the objective of this investigation is to evaluate the effect of boric acid as a set retarder on properties of geopolymer binder for its wider applications. It is found that the setting time of geopolymer paste enlarges with increment in dosage of boric acid. The extra water required for the optimum flow of geopolymer mortar was found about 20 %. The compressive strength properties of geopolymer mortar improve with the increase of boric acid. The optimum dosage of boric acid as set retarder was found 2 % of geopolymeric binder in present study. The results of this study will guide in effective use of boric acid as set retarder in geopolymeric material for its application of in-place casting and achieving the target of sustainable construction.

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