Strength Of Cementitious Materials Research Articles

Optimization of Cementitious Material with Thermal-Activated Lead-Zinc Tailings Based on Response Surface Methodology.

The accumulation of lead-zinc tailings will cause a series of problems, including geological disasters and environmental pollution. Efficient secondary utilization of lead-zinc tailings is crucial. In this study, the activity of lead-zinc tailings was stimulated by thermal activation. The optimal thermal activation parameters are a thermal activation temperature of 900 °C and a holding time of 30 min. Based on the response surface methodology, the effect of raw materials content on cementitious material strength was analyzed, and the relational model between cementitious material strength and experimental variables was established. The results show that the sensitivity order of cementitious material strength at 28 days curing age is sand/cement ratio > water/cement ratio > fly ash content > tailing content. According to the relational model, the optimal materials ratio is as follows: tailing/fly ash/cement = 28.99%:14.58%:56.43%, and the sand/binder ratio and water/binder ratio are 1:1 and 0.47, respectively. The corresponding cost is CNY 290.965 per ton, which is the lowest. The strength of cementitious material with these parameters can reach 20 MPa, which meets the requirements of "Technical specification for application of solid waste cementitious material (T/CECS 689-2020)".

Influence of Paste Strength on the Strength of Expanded Polystyrene (EPS) Concrete with Different Densities.

Concrete in which EPS (expanded polystyrene) particles partially or completely replace concrete aggregates is called EPS concrete. Compared to traditional concrete, EPS concrete has a controllable low density and good thermal-insulation performance, which make it promising for prospective applications. At present, research on EPS concrete mostly focuses on increasing its strength and EPS surface modifications. Few researchers have studied the influence of cementitious material strength and EPS-concrete density on the strength of EPS concrete. In this research, cement was used as the main material, and fly ash, silica fumes, and blast furnace slag were selected as admixtures. By changing the mixing proportions of the admixtures, the basic properties, such as the paste strength, change. Based on the mix proportions of the above different raw materials, EPS concrete with different density levels was prepared to explore the influence of the density of EPS concrete and the strength of cementitious materials on the strength of EPS concrete. The influence of the slurry strength on EPS-concrete strength was weaker than that of the density of EPS concrete. When the strength range of the cementitious materials is 35.7~70.5 MPa, the compressive strength range of 1000 kg/m3, 1200 kg/m3, and 1400 kg/m3 EPS concrete is 8.8~17.6 MPa, 11.4~18.0 MPa, and 15.7~26.6 MPa, respectively. Based on the experiments, the fitting equation to determine the EPS-concrete strength–EPS-concrete density–cementitious material strength is z = 69.00087 + 0.0244x − 0.1746y − 0.00189x2 + 0.0000504706y2 + 0.00028401xy. Additionally, a strength-increasing design method for EPS concrete with different densities prepared by conventional Portland cement is clarified. This study can guide the preparation of EPS concrete.

Effects of curing temperature on shear behaviour of cemented paste backfill-rock interface

Understanding the shear behaviour of the interface between rock and cemented paste backfill (CPB) is critical for the cost-effective geotechnical design of underground CPB structures. Curing temperature is one of the key factors that can affect the shear behaviour and resistance of the CPB-rock interface. However, no studies have been performed to investigate its effects on the shear behaviour of the interface between rock and tailings backfill that is undergoing cementation. The main objective of this study is to therefore experimentally study the effects of three different curing temperatures (2 °C, 20 °C, and 35 °C) on the shear behaviour and strength of the CPB-rock interface. The obtained results show that higher curing temperatures (up to 35 °C in this study) can increase the rate of cement hydration and self-desiccation, thus increasing the peak shear stress at the interface between early age CPB and rock. However, the sample cured for a longer time of 28 days at a higher temperature of 35 °C has a lower shear strength than that cured at a lower temperature of 20 °C. This lower shear strength is due to the crossover effect, which is the phenomenon of temperature inversion in the strength of cementitious materials. The findings presented in this paper will contribute to a better assessment of the stability of backfill structures and a better design for them.

Discrete Model for the Structure and Strength of Cementitious Materials

Cementitious materials are characterized by brittle behavior in direct tension and by transverse dilatation (due to microcracking) under compression. Microcracking causes increasingly larger transverse strains and a phenomenological Poisson’s ratio that gradually increases to about $$\nu =0.5$$ and beyond, at the limit point in compression. This behavior is due to the underlying structure of cementitious pastes which is simulated here with a discrete physical model. The computational model is generic, assembled from a statistically generated, continuous network of flaky dendrites consisting of cement hydrates that emanate from partially hydrated cement grains. In the actual amorphous material, the dendrites constitute the solid phase of the cement gel and interconnect to provide the strength and stiffness against load. The idealized dendrite solid is loaded in compression and tension to compute values for strength and Poisson’s effects. Parametric studies are conducted, to calibrate the statistical parameters of the discrete model with the physical and mechanical characteristics of the material, so that the familiar experimental trends may be reproduced. The model provides a framework for the study of the mechanical behavior of the material under various states of stress and strain and can be used to model the effects of additives (e.g., fibers) that may be explicitly simulated in the discrete structure.

The effects of superabsorbent polymers on the microstructure of cementitious materials studied by means of sorption experiments

Superabsorbent polymers (SAPs) are a promising additive to be used in the building industry but may induce microstructural changes. Water vapour sorption may be used to characterize the change in pore structure of cementitious materials, but the technique is difficult to interpret. In the present paper, static and dynamic vapour sorption (DVS) measurements were performed and compared to nitrogen adsorption experiments. The models of Dubinin-Radushkevich and Barrett-Joyner-Halenda were hereby applied to study pores in the micro- and mesopore range. The results show that cement pastes with SAPs and without additional water show a slight decrease in porosity in the micro- and mesopore range. Cement pastes with SAPs and with additional water show no significant change of porosity in the micropore range and a slight increase in the larger mesopore range. These new findings give insight into the effects of SAPs on the microstructure and strength of cementitious materials.

Efficiency of Scrap Rubber Particles on Strength of Cementitious Materials

An extensive research programme was set up to investigate the efficiency of scrap rubber particles on strength of cementitious materials. The index of strength loss rate of paste and mortar sample caused by increasing 1% volume rubber particles was proposed to analyze the efficiency of rubber particles in cementitious materials. And the corresponding mechanism was also discussed in this paper. Results indicate that in the investigated area, the loss rate in compressive strength both for paste and mortar almost ranges from 2% to 5% caused by increasing 1% rubber particles depending on the total volume of rubber particle added into sample. However, the loss rate in flexural strength of mortar by increasing 1% volume rubber particles is obviously different from that. Three roles of scrap rubber particles played in cementitious materials, named as deformation effect, equivalent-pore effect and hydrophobic effect, are responsible for the efficiency of scrap rubber particles on strength of cementitious material. The efficiency of rubber particles on strength of paste and mortar differs from each other due to the different microstructure between paste and mortar.

Chaotropic substances and their effects on the mechanical strength of Portland cement-based materials

Portland cement-based materials are present in our everyday life. Over the last two decades, important developments have been made to improve their mechanical strength, mainly through microstructural design. In addition, another promising parameter still remains in the early stages of understanding: that of adhesion. Recently, interdisciplinary researchers have considered the issue of water confinement by the hydrated cementitious surfaces. It could contribute to increase the adhesion and strength in these materials. On the other hand, ionic and nonionic chaotropic substances might be able to disorder the structure of such special water. The results presented in this paper show important effects of these chaotropic substances on the strength of cementitious materials. They highlight the role of the confined water on the adhesion, when the microstructural parameters are kept constant. More than contributing to the fundamental understanding of adhesion within cement paste, these results provide basic insights on in-situ nanotechnology.

Size effect: Influence of proximity of fracture process zone to specimen boundary

Size effect on strength of cementitious materials was studied successfully many years ago by a crack-bridging model through detailing the influence of the resistance R-curve behaviour on quasi-brittle fracture. The condition that specimens of different sizes have to be geometrically similar, commonly assumed for size effect study, was proven unnecessary. The present study emphasizing the interaction between the fracture process zone and structure boundary agrees with the crack-bridging analysis, and further points out that physical size itself is not the key mechanism for the apparent size effect.

Behavior of cementitious materials for high-strain rate conditions

An experimental study aimed at characterization of the combined effects of confinement and high strain rate on the deformation and strength of cementitious materials was conducted. Quasi-static triaxial compression tests for confining pressures ranging from 0 to 6.89 MPa were performed. Dynamic tests for strain rates in the range 40/s to 160/s, under unconfined and confined conditions, were conducted using a split Hopkinson pressure bar. A decrease in strain rate sensitivity with increasing confining pressure was observed. The materials susceptibility to damage under shear loading appears to be more a function of confinement than loading rate. Also, though the uniform stress requirements were not met under uniaxial conditions, minimal levels of confinement yielded valid constitutive property data over the majority of the duration of the experiments.