Showing papers on "Cement published in 2021"

Effects of fineness and content of phosphorus slag on cement hydration, permeability, pore structure and fractal dimension of concrete

Abstract: The utilization of phosphorus slag (PHS) to replace the fly ash in the construction of hydraulic projects has attracted a growing attention in China. In this study, the influence of PHS fineness an...

Technological performance of açaí natural fibre reinforced cement-based mortars

Abstract: Acai (Euterpe oleracea Mart.) is a fruit from forests typical of South American countries, such as Brazil. The fruit is harvested from palm trees and later processed to produce several food and aesthetic products that bear considerable health benefits. The processing of acai generates substantial amounts of waste, such as natural fibres, which are generally disposed of in landfills. The objective of this work is to evaluate the technological performance of adding acai fibre (with additions of 1.5%, 3.0% and 5.0% relative to cement mass) in its natural condition and after surface treatment with NaOH in mortars based on cement and lime. Acai fibre was physically, chemically and microscopically characterised. The properties of consistency, water retention, incorporated air content, mechanical strength (compression and flexion), mass density (fresh and hardened state), capillary water absorption and durability (wetting and drying cycles) were analysed as well. Results show that acai fibres in additions of up to 3.0% relative to cement mass and properly treated with NaOH solution can be used as reinforcement mechanism for mortar applications.

Biomass ashes from agricultural wastes as supplementary cementitious materials or aggregate replacement in cement/geopolymer concrete: A comprehensive review

Abstract: This paper aims to provide a comprehensive review of recent trends in incorporating biomass ashes from agricultural waste in Ordinary Portland cement (OPC) and geopolymer concrete. The material properties of different biomass ashes and their effect on fresh and hardened concrete properties (i.e., mechanical and durability properties) are reviewed. Partial replacement of OPC with byproducts, such as bamboo leaf ash, date palm ash, elephant leaf ash, banana leaf ash and plantain peel ash, rice straw ash, olive waste ash, wheat straw ash, and corn cob ash, escorts reduction in carbon dioxide (CO 2) emissions and global warming. It will also contribute to the effort of achieving zero-waste technology and sustainable development. This paper provides essential background information on the global status, composition, and ash preparation procedures of green and sustainable cementitious materials and then explores their potential applications. This review also highlights the areas requiring further research and indicates the possible negative impacts of utilizing these non-traditional supplementary cementitious materials (SCMs). The findings from this review confirm the feasibility of using biomass ashes as pozzolanic materials in cement concrete or as alternative activators in geopolymer concrete, with the required properties of building materials. Also, it is expected that this review will provide a better insight into biomass ashes incorporated in concrete for the benefit of academic/fundamental research and the construction industry.

Application of waste tire rubber and recycled aggregates in concrete products: A new compression casting approach

Abstract: The inferior performance of eco-friendly concrete owing to the addition of waste materials is a big hurdle in its practical adaptation. This study focuses on developing eco-friendly and green concrete, having performance similar to normal aggregate concrete (NAC). For this purpose, two waste products, including recycled aggregates (RA) and waste tire chipped rubber (CR), were used during the study. Furthermore, green concrete was also manufactured using RA treated through techniques such as lime immersion with carbonation and acetic acid immersion with mechanical rubbing. To achieve the strength of green concrete similar to NAC, an innovative concrete casting approach was followed. Green concrete specimens were cast and then compressed in the fresh state using specially designed molds. Results show that the compressive strength of recycled aggregate concrete (RAC) incorporating 20% CR in replacement of coarse aggregates is noticed 49% lower than NAC. However, the compressive strength and elastic modulus of compressed RAC and treated RAC incorporating 10-20% of CR in replacement of coarse aggregates are quite close to traditional concrete specimens without CR. No such method is available in the current literature through which green concrete incorporating RA and CR can achieve properties similar to NAC. Furthermore, the cost comparison and cement strength contribution index calculated in this study also show the industrial application potential of the new casting approach. Therefore, the developed concrete casting approach promotes the efficient utilization of RA and CR in the production of precast concrete members resulting in eco-friendly and sustainable construction.

Sustainable materials for 3D concrete printing

Abstract: This paper explores the sustainability aspects of binders used in concrete 3D concrete printing. Firstly, a prospective approach to conduct sustainability-assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing. The potential of the material production phase is emphasized to enhance the sustainability potential of 3DCP by reducing the embodied impacts. The literature on the different binder systems used for producing 3D printable mixtures is reviewed. This review includes binders based on portland cement and supplementary cementing materials (SCMs) such as fly ash, silica-fume and slag. Also, alternative binders such as geopolymer, calcium sulfo-aluminate cement (CSA), limestone calcined clay cement (LC3) and reactive magnesium oxide systems are explored. Finally, sustainability assessment by quantifying the environmental impacts in terms of energy consumed and CO2 emissions of mixtures is illustrated with different binder systems. This paper underlines the effect of using SCMs and alternative binder systems for improving the sustainability of 3D printed structures.

Recent progress of utilization of activated kaolinitic clay in cementitious construction materials

Abstract: The development of a green alternative that can partially or completely substitute the Ordinary Portland cement (OPC) as a practical construction material with low CO2 footprint is an important subject to researchers for decades. The use of artificial pozzolanic materials, e.g. fly ash, slag, silica fume, etc. cannot meet the huge-scale demand for cement replacement. Kaolinitic clay, with its high pozzolanic reactivity after activation and abundant resources worldwide, is regarded as a promising supplementary cementitious material (SCM) for cement. Recent studies have addressed that the utilization of calcined kaolinitic clay as SCM can effectively improve the properties of cement products. This paper presents a comprehensive review of the research progress on activated kaolinitic clay as SCM in the last decade. It systematically introduces the essential properties, activation mechanism and pozzolanic reactivity assessment of kaolinitic clay. Application of calcined clay in two different cementitious systems (calcined clay blended cement and limestone calcined clay cement) is reviewed from the aspects of workability, mechanical properties, and long-term durability properties with the mechanism discussion. Finally, the environmental and economic impacts of the application of calcined clay in different cementitious systems are discussed.

Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing.

Abstract: This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor—KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

Abstract: Magnesium oxysulfate (MOS) cement is a typical eco-friendly cementitious material, which presents excellent performances. In this work, a novel multiscale modeling strategy is proposed to simulate the hydration and pore structure of MOS cement system. This work collected and evaluated the Gibbs free energy of formation for main hydrates and equilibrium constant of main reactions in MOS cement system based on a first principle calculation using Material Studio. Followingly, the equilibrium phase compositions of MOS cement system were simulated through PHREEQC to investigate the molar ratio dependence of equilibrium phase compositions. Results showed that large M (MgO/MgSO4) was beneficial for the formation of 5Mg(OH)2·MgSO4·7H2O (Phase 517) and large H (H2O/MgSO4) tended to decompose MOS cement paste and cause leaching. The microstructure-based method visualized the hydration status of MOS cement systems at initial and ultimate stages via MATLAB and the results showed that large M was significant to reduce porosity, and similar results for the case of small H. Fractal analysis confirms that fractal dimension of pore structure (Df) was significantly decreased after the hydration of MOS and was positively correlated to the porosity of the paste. In addition, it can be referred that large M and small H were beneficial for modifying the microstructure of MOS paste by decreasing the value of Df.

Environmental sustainability in cement industry: An integrated approach for green and economical cement production

Abstract: The carbon footprint of cement industries has been a major environmental issue in recent decades. Carbon Capture and Storage (CCS), use of Supplementary Cementing Materials (SCMs) as partial replacement to cement, and use of nanotechnology are some approaches that are being tested and practiced for reducing the carbon dioxide (CO2) emissions from the cement industries. Each of these approaches, however, comes with their own limitations and the implementation in real industrial scenarios is yet a concern. This paper proposes an integrated approach where CO2 captured from cement plant will be utilized within the plant for producing nano calcium carbonate (CaCO3) for use in cement manufacturing process. This technology incorporates all the above three approaches and help cement industries produce sustainable, durable, and economical cement while reducing the CO2 emissions into the atmosphere: thus, leading towards green infrastructure and global environmental sustainability. Additionally, adoption of this technology ensures proper dispersion of nano materials thereby improving the performance of concrete. Further, this technology is economically attractive to cement industries as they will have a new product (nano CaCO3) with much higher cost than cement with potential of additional economic revenues.

State-of-the-art-review on rice husk ash: A supplementary cementitious material in concrete

Abstract: Rice husk ash (RHA) is a good supplementary cementitious material for concrete production, as it requires low energy and emits negligible greenhouse gas during processing and service life as well as it shows high pozzolanic reactivity. The pozzolanic reactivity of RHA depends on its amorphous silica content, fineness, mix proportion, available alkaline media, and temperature because all of these factors are related to the dissolution of silica from RHA. Thus, incineration time, temperature, processing, and grinding of RHA should be controlled to acquire the desired level of pozzolanic reactivity. Depending on the filler effect and pozzolanic reactivity of RHA, concrete’s strength varies. The RHA-blended cement concrete possesses dense microstructure, high mechanical performance, and enhanced durability against harsh environmental exposure. However, the cement replacement level by RHA should be within the optimum level, which is a factor of fineness and the mixed proportion of concrete. This review covered the current practice and guidelines of RHA-blended concrete. Simultaneously, this review also revealed a gap in in-depth investigations about the long-term durability and serviceability of reinforced RHA-blended concrete. Further research could lead to the application of RHA as a cost- and environmentally competitive alternative in the production of high-performance concrete. The summary and discussions provided in this paper will provide both direction and knowledge on the applications of greener and more sustainable RHA-blended concrete for researchers.