Showing papers on "Cement published in 2020"

Silica fume and waste glass in cement concrete production: A review

Abstract: The vast emission of greenhouse gases from industrial wastes is a global problem. The non-biodegradable nature of industrial wastes like silica fume , glass, bottom ash, and rubber tyres increases the severity of the problem. Past studies suggest that the use of waste materials in the cement and construction industry could be a viable solution to prevent natural resources from extinction. The chemical composition of silica fume and waste glass are attracting cement and concrete industries as a sustainable solution. In recent years, green concrete is very popular among researchers and academicians, but green concrete is still at an early stage. This paper studies the influence of silica fume and waste glass on the workability, strength, and durability properties of concrete . Moreover, the microstructural analysis was also studied.

Prediction of concrete strength in presence of furnace slag and fly ash using Hybrid ANN-GA (Artificial Neural Network-Genetic Algorithm)

Abstract: Mineral admixtures have been widely used to produce concrete. Pozzolans have been utilized as partially replacement for Portland cement or blended cement in concrete based on the materials' properties and the concrete's desired effects. Several environmental problems associated with producing cement have led to partial replacement of cement with other pozzolans. Furnace slag and fly ash are two of the pozzolans which can be appropriately used as partial replacements for cement in concrete. However, replacing cement with these materials results in significant changes in the mechanical properties of concrete, more specifically, compressive strength. This paper aims to intelligently predict the compressive strength of concretes incorporating furnace slag and fly ash as partial replacements for cement. For this purpose, a database containing 1030 data sets with nine inputs (concrete mix design and age of concrete) and one output (the compressive strength) was collected. Instead of absolute values of inputs, their proportions were used. A hybrid artificial neural network-genetic algorithm (ANN-GA) was employed as a novel approach to conducting the study. The performance of the ANN-GA model is evaluated by another artificial neural network (ANN), which was developed and tuned via a conventional backpropagation (BP) algorithm. Results showed that not only an ANN-GA model can be developed and appropriately used for the compressive strength prediction of concrete but also it can lead to superior results in comparison with an ANN-BP model.

Performance of recycled aggregate concrete with rice husk ash as cement binder

Abstract: This research aims to utilize rice husk ash as a cementitious materials in recycled aggregate concrete (RAC). Rice husk ash was ground until the particles remained on a No. 325 sieve were 4.6%wt. Then, the ash was used to partially replace cement at 20 to 50%wt of binder to cast concrete. The compressive strength, steel corrosion, and chloride penetration depth by the impressed voltage method of RAC were examined. The results revealed that the replacement of 20% of ordinary Portland cement (OPC) by ground rice husk ash (GRHA) enhances the compressive strength of the RAC to be greater than the RAC without GRHA at 60 days. Concrete with GRHA at 20 to 50%wt of binder significantly improved the steel corrosion and chloride resistance of the RAC. The utilization of GRHA at 50% to replace OPC gave the highest chloride penetration resistance and produced the lowest steel corrosion of the RAC. Although, the RAC with GRHA had less compressive strength than CT concrete, the concrete provided a positive effect of increasing the resistance of chloride penetration and lowering steel corrosion.

Accelerated carbonation of reactive MgO and Portland cement blends under flowing CO2 gas

Abstract: The use of MgO-based materials for sequestration of CO2 offers technical advantages and environmental incentives. However, the understanding of accelerated carbonation of MgO-based materials in flowing CO2 gas is limited. This study elucidates the carbonation behaviour of reactive MgO cement (MC) and MgO-Portland binary cement (BC) in a simulated CO2-rich industrial exhaust. Quantitative X-ray diffraction and thermogravimetric analyses showed that nesquehonite (MgCO3·3H2O) was the major carbonation product in MC pastes, whereas CaCO3 was preferentially generated in BC pastes. The relative humidity of exhaust gas influenced CO2 diffusion and the carbonation rate; 98% humidity facilitated MC carbonation whereas 50% was favourable for BC carbonation. Although CO2 concentration determined the carbonation rate, 10% CO2 gas in the exhaust was sufficient to accelerate carbonation. The carbonation degree and compressive strength of samples cured for 7 days at 10% CO2 were comparable to the values of samples cured for 1 day at 100% CO2. The presence of acid gases during CO2 curing inhibited the carbonation and hydration processes, but the presence of Portland cement in the BC system gave good compatibility with acids and relieved the inhibitory effect. Desulphurization and denitrification of industrial exhaust gas are nonetheless desirable before CO2 curing. This study builds the foundation for utilising industrial CO2 exhaust to accelerate the carbonation of Mg-based materials.

Effects of water content, water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

Abstract: The pumping ability and placement performance of fresh cemented paste backfill (CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement (PC), a newly released commercially manufactured cement called Minecem (MC) and fly ash (FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature (25 °C), with regards to the unconfined compressive strength (UCS) performance, the replacement of 4% PC mixed CPB (28 days UCS 425 kPa) to 3% MC mixed CPB (28 days UCS 519 kPa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water (MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.

Toward electrochemical synthesis of cement-An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams.

Abstract: Cement production is currently the largest single industrial emitter of CO2, accounting for ∼8% (2.8 Gtons/y) of global CO2 emissions. Deep decarbonization of cement manufacturing will require remediation of both the CO2 emissions due to the decomposition of CaCO3 to CaO and that due to combustion of fossil fuels (primarily coal) in calcining (∼900 °C) and sintering (∼1,450 °C). Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO3 is decarbonated at low pH and Ca(OH)2 is precipitated at high pH, concurrently producing a high-purity O2/CO2 gas mixture (1:2 molar ratio at stoichiometric operation) at the anode and H2 at the cathode. We show that the solid Ca(OH)2 product readily decomposes and reacts with SiO2 to form alite, the majority cementitious phase in Portland cement. Electrochemical calcination produces concentrated gas streams from which CO2 may be readily separated and sequestered, H2 and/or O2 may be used to generate electric power via fuel cells or combustors, O2 may be used as a component of oxyfuel in the cement kiln to improve efficiency and lower CO2 emissions, or the output gases may be used for other value-added processes such as liquid fuel production. Analysis shows that if the hydrogen produced by the reactor were combusted to heat the high-temperature kiln, the electrochemical cement process could be powered solely by renewable electricity.

Reuse of waste glass as a supplementary binder and aggregate for sustainable cement-based construction materials: A review

Abstract: Safe disposal of the huge amount of waste glass has become a serious environmental concern in many countries. On the other hand, production of concrete uses huge amount of natural resources and adds greenhouse gases to the environment. Therefore, researchers have been working on the reuse of waste glass as a supplementary cementitious material (SCM) and aggregate in the production of cement mortar and concrete. This paper reviews the mechanical and durability properties of mortar and concrete using waste glass as partial replacements of cement and natural sand. The optimum proportions of waste glass as in cement based construction materials in different ways have been identified and critically discussed by the analysis of experimental data available in various published literatures. It was found that the properties of glass powder blended cement mortar or concrete are mainly dependent on several factors such as particle size, replacement level, colour and type of the glass and curing age and curing temperature. The use of glass powder significantly improved the mechanical and durability properties of cement mortar and concrete when the particle size of glass powder is less than 45 μm and cement replacement rate is about 10–40%. It was also observed that glass fine aggregate can be used as up to 100% of the fine aggregate in mortar and concrete without negative effects on mechanical and durability properties when the particle size is less than 1 mm. The combined use of glass as SCM and fine aggregate reduced the mechanical properties of cementitious systems ; however, improved some durability properties. Moreover, the current research progress on waste glass mixed cementitious systems is critically reviewed and some future research is recommended.