Early Strength Of Mortar Research Articles

Exploring the effect of self-combustion gangue powder particle distribution on rheological behavior and hydration mechanism in cement-based systems

Solid waste-based mineral admixtures are widely employed as a partial replacement for Portland cement due to their superior performance and minimal carbon and environmental footprint. This study involves the production of self-combustion gangue powder (SCGP) with varying particle sizes achieved through crushing, screening, and grinding. The SCGP is subsequently blended with cement to form a self-combustion gangue powder-cement (SCGP-C) system with diverse particle size distribution. Rheological tests and hydration exothermic tests were conducted to investigate the rheological behavior and degree of hydration of the SCGP-C mixed system. The results show that SCGP enhances the plastic viscosity and thixotropy of the mixed slurry. However, when a finer SCGP (d50=1.36 μm) was used to replace 15 % of the cement for the same mass, the yield stress and rheological index of the slurry were reduced by 28.1 % and 15.4 % respectively compared to the control group, while the closed-packing of the SCGP-C system was obtained. When the cement was replaced by 15 % SCGP (mass substitution), the yield stresses of finer and coarser SCGP (d50=18.24 μm) and pure cement slurries were increased by 289.1 %, 67.3 %, and 29.2 %, respectively, at T=60 min compared to T=0 min. This suggests that the fineness of SCGP has a greater effect on the yield stresses of mixed slurries over time. Mixed slurries with different finenesses of SCGP all prolonged the hydration induction period and reduced the total exothermic heat of hydration. Incorporating 15 % finer SCGP extended the induction period of the mixed slurry by 27 min and increased the peak value of the main hydration curve. Appropriate incorporation of SCGP helps to improve the fluidity and early strength of mortar in the SCGP-C system and promotes the physical filling effect and the positive role of SCGP volcanic ash in the cement system.

Experimental Study on Sulfate Attack Resistance of Cement Slurry with UEA Expansive Agent

Sulfate attack was one of the most important factors affecting the durability of cement slurry in mine corrosive environment. For water stopping and reinforcement projects in wellbore or working face under sulfate erosion environment, mineral admixtures were often used to improve the sulfate resistance of cement slurry. The physical and mechanical properties of cement mortar with 0, 4%, 8%, 12% and 16% UEA expansive agent content under the conditions of 0.6%, 3% and 15% sodium sulfate solution concentration were investigated through the full immersion test for 19 months in the laboratory. The results showed that the strength of mortar specimens decreased with the increase of UEA expansive agent content, but in the sulfate attack environment, the ability to resist sulfate attack could be significantly improved. In order to ensure the early strength of mortar and reduce the cost, the best effect of UEA expansion agent was 4%.

Effect of boron-containing aggregates on setting and hardening of Portland cement mortars

Multicomponent cement-based composites are known as versatile structural materials for enhanced radiation shielding. The use of selected elements, like boron, cadmium, or rare earth elements, provides an increased neutron shielding capacity. Because of profusion, reasonable costs and large cross-section for neutron capture, boron containing minerals are suggested as aggregates for radiation shielding concrete. Despite many advantages, boron additives may act as cement setting retarders. Uncontrolled setting and hardening is not acceptable in radiation shielding concrete technology. In this work we present results from isothermal calorimetry measurements on cement mortars with boron-containing aggregates. Four types of boron aggregates were used in the studies: colemanite, ulexite, borax and boron carbide. Based on calorimetric curves, the beginning of setting time was determined. Additionally early mortar strength was investigated and linear relationship between the heat generated in the isothermal calorimeter and the early compressive strength has been observed. The use of isothermal calorimetry allowed us to estimate the limits for the content of boron compounds to be used cement mortar.

Microstructure and Properties of C-S-H/PCE Nanocomposites

Different dosage of TPEG-polycarboxylate (PCE) copolymers were used to prepare the calcium-silicate hydrated (C-S-H)/PCE nanocomposites by precipitating C-S-H from Na2SiO3·9H2O and Ca (NO3)2·4H2O in the PCE solution. The composition and structure of the prepared C-S-H/PCE nanocomposites were characterized by XRD, SEM, FTIR methods, and the early strength of mortars was measured. The results show that structural investigation of the C-S-H/PCE nanocomposites via X-ray diffraction revealed a semi-crystalline composition, and the PCE polymers were adhered the surface of C-S-H particles in the composite. The preparation of C-S-H /PCE nanocomposites enhanced markedly the early strength of mortar, and when the dosage of PCE copolymers was up to 30%, the early strength enhancing effect was the highest, the early flexural strength increased up to 100%, and early compressive strength increased up to 120%. Therefore, C-S-H /PCE nanocomposites can improve the early strength of mortar effectively since it can lower the barrier of nucleation of the products, promote the nucleation and inhibit the growth of large grains effectively.

Activity of calcined coal gangue fine aggregate and its effect on the mechanical behavior of cement mortar

In order to reveal the influence of coal gangue aggregate activity on the mechanical properties of the mortar, to promote coal gangue fine aggregate in concrete mortar application, this paper in view of the calcined coal gangue aggregate carried out ion dissolution test (ICP), construction of the coal gangue aggregate ion dissolution amount and its surface area ratio as a quantitative index of activity, namely activity index of Ka. The different fineness modulus, different curing age of concrete mortar carried out compressive strength and flexural strength test, and the hardening of cement mortar combined with microscopic test results, in order to analyze the influence of coal gangue aggregate activity on the mechanical performances of mortar. Experimental results show that, under the same calcination temperature and surface area of coal gangue fine aggregate with the same ion dissolution ability, coal gangue fine aggregate index activity increases with the gradual decrease of fineness modulus. A higher activity index of coal gangue fine aggregate mortar corresponds to higher compressive strength and flexural strength of mortar in the improved macro mechanical properties; the early strength of mortar has clear characteristics.

Application of Sanming Steel Slag Powder in Cement and Concrete

Effects of steel slag powder on properties of cement and concrete are investigated. Results show that with the increase of steel slag power, water requirement of normal consistency is decreased, and the setting times are prolonged. The early mortar strength is lower, but late strength rate of increase is great. Steel slag powder is compatible with blast furnace slag. Moreover，concrete，which has harmonious development strength and excellent workability can be obtained by mineral additives two-element compounding.

Studies on mortars containing waste bottle glass and industrial by-products

This study presents investigation of properties of cement-based mortars produced with cement containing waste glass (WG) and industrial by-products. The features, compressive strength, sulfate and chloride resistance, high temperature resistance, and expansions related to alkali–silica reaction (ASR) are examined. Three series of mortar specimens containing ground WG are prepared. Only ground WG is replaced cement in the first series. Ground WG, ground granulated blast-furnace slag (GGBFS) or fly ash (FA) is replaced cement in the second and third series. The results showed that compressive strength was decreased as replacement level increased. The observed losses in early strength of mortars were relatively higher than strength losses measured at 28th day. Minor increases in strength were obtained at 10% and tolerable decreases in strength were observed at 30% replacement levels. The same trend is also valid for durability properties examined in this study. Hence it is concluded that combined usage of WG and GGBFS, or WG and FA will be more suitable instead of using WG alone in mortar.

The effect of pectin on the physicochemical and mechanical properties of cement containing boron

The effects of varying concentrations of pectin (0.1–1 wt% of cement) on the properties of ordinary portland cement (PC) and cement containing colemanite ore waste (CW) were investigated. Variation in setting time, compressive strength, and volume expansion of hydrated specimens were determined. It was found that pectin acts as an accelerator for PC cement and as a retarder for CW cement at a level below 0.1%. The inclusion of pectin in PC resulted in a reduction in the early strength of the mortar. However, pectin had positive contribution to the early compressive strength of the CW mortar. The hydration products were also identified by means of X-ray diffraction (XRD) and their microstructure by scanning electron microscopy (SEM). Although the observed hydration products were mostly as expected, due to presence of pectin in the cement paste, the degree to which these phase was present was unusual. In particular, the relative intensity of calcium hydroxide peaks decreased with the increasing pectin content at 2 days curing age.