Flowability and Strength Characteristics of Binary Cementitious Systems Containing Silica Fume, Fly Ash, Metakaolin, and Glass Cullet Powder

The present study examines the effects of supplementary cementitious materials (SCMs) on the flowability and strength development of binary mixes. This study was primarily motivated by the need to bridge the knowledge gap regarding paste and mortar mixes containing binary cement from a variety of performance perspectives. This study examined the flowability and strength development of binary mixes in their pastes and mortars when they contain various doses of silica fume (SF), fly ash (FA), metakaolin (MK), and glass cullet powder (GP) compared with the control mix. While the presence of SF and MK reduced workability because of the nature of their particles, the addition of FA and GP improved it to a certain extent because of the spherical and glassy nature of their particles, respectively. In addition, GP was used to compare its performance against SF, MK, and FA as an alternative cementitious material. In this study, the GP performed comparably to the other SCMs investigated and was found to be satisfactory. An investigation of the rheological properties, heat of hydration, thermal analysis, and pore systems of these mixes was conducted. Compared to the control mix, the presence of 5% GP improved the rheological properties and reduced the heat of hydration by 10%. The reduced workability in SF and MK mixes resulted in a lower content of pore water, while GP and FA incorporation enhanced it, owing to improved workability. The pore area is related to the pore water, which is directly related to improved workability. According to the following order, SF > MK > GP > FA, the strength was highest for mixes containing SF and MK, whereas, with GP and FA, there was a gradual reduction in the strength proportional to replacement level and improved workability. SF, GP, and FA can be identified as performance enhancers when formulating ternary and quaternary cementitious systems for low-carbon cement.

Alkali-Activated Materials Doped with ZnO: Physicomechanical and Antibacterial Properties

The requirements related to reducing the carbon footprint of cement production have directed the attention of researchers to the use of waste materials such as blast-furnace slag or fly ashes, either as a partial replacement for cement clinker or in the form of new alternative binders. This paper presents alkali-activated materials (AAMs) based on blast-furnace slag partially replaced with fly ash, metakaolin, or zeolite, activated with water glass or water glass with a small amount of water, and doped with zinc oxide. The mortars were tested for flow, hydration heat, mechanical strength, microstructure, and antimicrobial activity. The obtained test results indicate the benefits of adding water, affecting the fluidity and generating a less porous microstructure; however, the tested hydration heat, strength, and antibacterial properties are related to more favorable properties in AAMs produced on water glass alone.

Effect of Sodium Gluconate on Properties and Microstructure of Ultra-High-Performance Concrete (UHPC)

The properties of concrete can be significantly affected by sodium gluconate (SG) at very small dosages. In this paper, the effects of SG on the fluidity, setting time, heat of hydration, and strength of ultra-high-performance concrete (UHPC) were studied. The results show that (1) in the plastic stage, SG inhibited the formation of early ettringite (AFt) and delayed the hydration of tricalcium silicate (C₃S) and dicalcium silicate (C₂S). SG increased the initial fluidity of UHPC without decreasing within 1 h. When the SG dosage was ≥0.06%, the slumps at 30 min and 60 min increased slightly. (2) In the setting hardening stage, the addition of SG inhibited the formation of calcium hydroxide (CH), which significantly extended the setting time of UHPC. When the dosage of SG was 0.15%, the initial and final setting times were 5.0 times and 4.5 times that of the blank group, respectively. SG had no obvious effect on the hydration rate of cement in the accelerated period, but the peak hydration temperature of UHPC was increased when the SG dosage was 0.03~0.12%. (3) In the strength development stage, the 1 d and 3 d strength of UHPC decreased significantly with the increase in the SG dosage. However, SG could promote the formation of AFt at the pores and aggregate interface in the later stage, reduce the porosity of cementite, and improve the compressive strength of UHPC in 28 d, 60 d, and 90 d. When the SG dosage was 0.12%, the 90d strength increased by 13%.

Effect of Hydration Temperature Rise Inhibitor on the Temperature Rise of Concrete and Its Mechanism

The rapid drop in internal temperature of mass concrete can readily lead to temperature cracks. Hydration heat inhibitors reduce the risk of concrete cracking by reducing the temperature during the hydration heating phase of cement-based material but may reduce the early strength of the cement-based material. Therefore, in this paper, the influence of commercially available hydration temperature rise inhibitors on concrete temperature rise is studied from the aspects of macroscopic performance and microstructure characteristics, and their mechanism of action is analyzed. A fixed mix ratio of 64% cement, 20% fly ash, 8% mineral powder and 8% magnesium oxide was used. The variable was different admixtures of hydration temperature rise inhibitors at 0%, 0.5%, 1.0% and 1.5% of the total cement-based materials. The results showed that the hydration temperature rise inhibitors significantly reduced the early compressive strength of concrete at 3 d, and the greater the amount of hydration temperature rise inhibitors, the more obvious the decrease in concrete strength. With the increase in age, the influence of hydration temperature rise inhibitor on the compressive strength of concrete gradually decreased, and the decrease in compressive strength at 7 d was less than that at 3 d. At 28 d, the compressive strength of the hydration temperature rise inhibitor was about 90% in the blank group. XRD and TG confirmed that hydration temperature rise inhibitors delay early hydration of cement. SEM showed that hydration temperature rise inhibitors delayed the hydration of Mg(OH)₂.

Managing the Heat Release of Calcium Sulfoaluminate Cement by Modifying the Ye'elimite Content

Nowadays, calcium sulfoaluminate cement (CSA) is garnering a large amount of attention worldwide and is being promoted as a sustainable alternative to Portland cement for specific applications. This study aimed to control the heat release of CSA cement paste by choosing the appropriate composition. For this purpose, different calcium sulfoaluminate clinkers with up to 75 wt. % of ye'elimite were synthetized. Then, a reactivity study on the synthesized clinkers was conducted while varying the amount of gypsum added. The heat of hydration was measured by isothermal calorimetry. The influence of the ye'elimite content on the heat release and on the compressive strength was investigated. According to the findings, the amount of ye'elimite in the cement has a direct relationship with the heat release. The heat release as well as the mechanical performance increase with the increase in the ye'elimite content in the CSA cement. An equation allowing the prediction of the total heat release after 24 h is provided. Such data can be of particular interest to consultants aiming at the reduction of thermal cracking in massive concrete.

Investigating the Potential Use of Date Kernel Ash (DKA) as a Partial Cement Replacement in Concrete

The palm and date sector is one of the most important sectors in Saudi Arabia. The total number of fertile palm trees in Saudi Arabia is about 31 million. In the production of pitted dates, date molasses, date paste, and date confectionery, a considerable number of date kernels are usually discarded as waste. This study reports experimental investigations conducted to evaluate the potential of waste date kernel ash (DKA), obtained by the calcination of date pits at 800 °C, as a partial cement replacement in concrete. DKA has low silica oxide and does not qualify as a pozzolanic material. The effect of DKA partially replacing the cement and acting as a filler material in concrete was investigated, and its properties were compared with two pozzolanic materials, fly ash (FA) and natural pozzolan (NP). Twelve concrete mixes in which cement was replaced with different proportions of calcined DKA (5%, 10%, 15%, 20%, and 30%), NP (10%, 20%, and 30%), and FA (10%, 20%, and 30%) were investigated in the experimental program. The properties of DKA, FA, and NP concrete mixes were evaluated in fresh and hardened states, including the heat of hydration, mechanical characteristics, and thermal properties. The results show that replacing cement with 5% date kernel ash increases the compressive strength by 0.42%, 3.2%, and 2.5% at 3, 7, and 28 days, respectively, while the 28-day compressive strength decreases by 2.4%, 5.4%, 16.3%, and 26.69% when the cement is replaced with 10%, 15%, 20%, and 30% DKA, respectively. Date kernel ash concrete mixes with 10%, 20%, and 30% replacement levels demonstrated higher compressive and tensile strengths and lower thermal conductivity, density, and workability when compared to natural pozzolan and fly ash. DKA is a promising partial cement replacement material; nevertheless, additional research is required to assess the durability of DKA in concrete.

Study on the Physical and Chemical Properties of Cement-Based Grout Containing Coal-Fly Ash

To study the physical and chemical properties of grout containing fly ash, Class II fly ash was used as a mineral admixture and mixed with silicate cement to produce grout, and the rheological properties, strength properties, hydration properties, and microscopic mechanism were studied. The results of the study showed the following. The incorporation of fly ash reduced the thixotropic area of the composite cement slurry, which facilitated pumping in the pipeline conveying process. The inclusion of fly ash reduced the yield stress and plastic viscosity of the cement paste, but the rheological index increased and then decreased with the increase in fly ash, and the composite paste had the lowest degree of shear thinning at 30% fly ash inclusion. The incorporation of fly ash reduced the hydration exothermic rate and total hydration exothermic amount of the composite slurry and prolonged the hydration induction period, but the promotion effect of fly ash on the hydration rate of cement was obvious at 10% fly ash admixture. The admixture of fly ash increased the empty volume of the composite slurry, but the effect on the most probable aperture was not significant, and the porosity of the system increased, resulting in a decrease in compressive strength. The effect of adding fly ash on the hydration products was reflected mainly by the C-S-H gel produced by cement hydration and the change in calcium alumina and Ca(OH)₂. Fly ash does not directly participate in the hydration reaction of cement, but it can promote cement hydration and increase the reaction rate of cement. By analyzing the rheological properties, mechanical properties, and hydration properties of fly ash composite cement paste, the comprehensive analysis found that the rheological properties are excellent when the fly ash admixture is 20-30%, and the water-cement ratio can be reduced to improve the strength without affecting the pumping demand.

Study of the Properties of Blended Cements Containing Various Types of Slag Cements and Limestone Powder

It is currently vital to use more environmentally friendly cementitious composites, such as blended slag-limestone cements. However, many properties of slag-limestone cements are not yet fully research, especially in regards to the effect of limestone properties on properties of mortars and concrete. In the research, three types of slag cements were mixed with two types of limestone to obtain multi-component slag-limestone cements. Tests of rheological properties, heat of hydration, and compressive strength were conducted to ascertain the effect of limestone on the cement properties and to check the viability of this type of cement for engineering practice. It was found that the addition of up to 10% of limestone to slag cements did not have negative effects on tested properties; however, the exact influence of limestone was dependent on limestone particle size distribution. Increasing the amount of limestone in limestone-slag cements to 15% significantly decreased the compressive strength of the mortars and decreased hydration heat but had no significant effect on rheological properties.

The Influence of Temperature on the Hydration Rate of Cements Based on Calorimetric Measurements

The study presents results of calorimetric tests of three different cements. Two Ordinary Portland cements, CEM I 52.5 R and CEM I 42.5 R, and one Blastfurnace cement, CEM III/A 42.5 N LH/HSR/NA, were analysed. The analysis has shown that the empirical formulas derived based on the results can successfully replace the Arrhenius formula in determination of the hydration rate in relation to curing temperature. It was proven that the hydration rate in relation to the curing temperature changes with the progression of hydration. The study introduces an E_n coefficient which determines the influence of curing temperature on generation of heat. Results of the study have shown that the value of E_n is not constant and changes with the progression of hydration process. Proposed method of numerical modelling of the total heat generated and generation rate based on obtained results allows for the calculation of those two parameters for any curing conditions.

Effects of Adding Neutralized Red Mud on the Hydration Properties of Cement Paste

Red mud is a highly alkaline waste by-product of the aluminum industry. Although recycling of red mud is being actively researched, a feasible technological solution has not been found yet. In this study, we propose that neutralization of red mud alkalinity could assist in its use as a construction material. Neutralized red mud (LRM + S; pH 6-8) was prepared by adding sulfuric acid to liquefied red mud (LRM; pH 10-12). After adding LRM and LRM + S to cement paste, the heat of hydration, compressive strength, and hydration products were examined. The experiments revealed that the calorific value of the cement paste with LRM was low, and its peak was delayed, when compared with that of plain cement paste (referred to as Plain), whereas the calorific value of the cement paste with LRM + S was similar to that of Plain. At the age of 28 d, the compressive strength of the cement paste with 10% LRM + S was 99% whereas that with 20% LRM was only 55% of the strength of Plain. Thus, our results help to resolve the issue of strength degradation of cementitious materials observed upon the addition of red mud and enable its reuse as a construction material.

A Study on the Reduction in Hydration Heat and Thermal Strain of Concrete with Addition of Sugarcane Bagasse Fiber

Early prevention methods in massive concrete structures to control the heat of hydration and, consequently, the development of cracks due to thermal expansion are important subjects, since these cracks may compromise structural integrity. In the present study, the sugarcane residues in massive concrete were used in order to investigate the reduction in the heat of hydration, the thermal expansion resistance, and also the fresh and mechanical properties of the concrete. The results showed that, by adding 2.0% of bagasse fiber and 5.0% of pozzolanic material to the concrete, the heat of hydration was reduced, and the strain due to the thermal expansion was smaller than the control mixture. Moreover, the compressive, flexural, and split tensile strength increased in comparison to the control mixture.

Strength Development and Thermogravimetric Investigation of High-Volume Fly Ash Binders

To address sustainability issues by facilitating the use of high-volume fly ash (HVFA) concrete in industry, this paper investigates the early age hydration properties of HVFA binders in concrete and the correlation between hydration properties and compressive strengths of the cement pastes. A new method of calculating the chemically bound water of HVFA binders was used and validated. Fly ash (FA) types used in this study were sourced from Indonesia and Australia for comparison. The water to binder (w/b) ratio was 0.4 and FA replacement levels were 40%, 50% and 60% by weight. Isothermal calorimetry tests were conducted to study the heat of hydration which was further converted to the adiabatic temperature rise. Thermo-gravimetric analysis (TGA) was employed to explore the chemically bound water (W_B) of the binders. The results showed that Australian FA pastes had higher heat of hydration, adiabatic temperature rise, W_B and compressive strength compared to Indonesian FA pastes. The new method of calculating chemically bound water can be successfully applied to HVFA binders. Linear correlation could be found between the W_B and compressive strength.

Influence of Cementitious System Composition on the Retarding Effects of Borax and Zinc Oxide

This research investigated the retarding impact of zinc oxide (ZnO) and borax (Na₂[B₄O₅(OH)₄]·8H₂O) on hydration of Portland cement, calcium aluminate cement (CAC), and calcium sulfoaluminate cement (CSA). Heat of hydration of cement paste samples with and without ZnO and borax was used to measure the influence of ZnO and borax on the set time of these cementitious systems. It was found that both ZnO and borax can retard the set time of Portland cement systems; however, ZnO was shown to be a stronger set time retarder than borax for these systems. ZnO did not show any retarding impact on CAC and CSA systems while addition of borax in these systems prolonged the set time. It was concluded that ZnO does not poison the nucleation and/or growth of CSA and CAC hydration products. We suggest that borax retards the cement set time by suppressing the dissolution of cement phases.

Complex Characterization and Behavior of Waste Fired Brick Powder-Portland Cement System

Two waste fired brick powders coming from brick factories located in Argentine and Czech Republic were examined as alternative mineral admixtures for the production of blended cements. In pastes composition, local Portland cements (Argentine and Czech) were substituted with 8–40%, by mass, with powdered ceramic waste. For the ceramic waste-Portland cement system, workability, the heat released, pozzolanity, specific density, compressive strength, hydrated phases, porosity, and pore size distribution were tested. The relevance of the dilution effect, filler effect, and pozzolanic activity was analyzed to describe the general behavior of the pozzolan/cement system. The properties and performance of cement blends made with finely ground brick powder depended on the composition of ceramic waste and its reactivity, the plain cement used, and the replacement level. Results showed that the initial mini-slump was not affected by a low ceramic waste replacement (8% and 16%), and then it was decreased with an increase in the ceramic waste content. Brick powder behaved as a filler at early ages, but when the hydration proceeded, its pozzolanic activity consumed partially the calcium hydroxide and promoted the formation of hydrated calcium aluminates depending on the age and present carbonates. Finally, blended cements with fired brick powder had low compressive strength at early ages but comparable strength-class at later age.

Revisiting the Effect of Slag in Reducing Heat of Hydration in Concrete in Comparison to Other Supplementary Cementitious Materials

Blast furnace slag (SL) is an amorphous calcium aluminosilicate material that exhibits both pozzolanic and latent hydraulic activities. It has been successfully used to reduce the heat of hydration in mass concrete. However, SL currently available in the market generally experiences pre-treatment to increase its reactivity to be closer to that of portland cement. Therefore, using such pre-treated SL may not be applicable for reducing the heat of hydration in mass concrete. In this work, the adiabatic and semi-adiabatic temperature rise of concretes with 20% and 40% SL (mass replacement of cement) containing calcium sulfate were investigated. Isothermal calorimetry and thermal analysis (TGA) were used to study the hydration kinetics of cement paste at 23 and 50 °C. Results were compared with those with control cement and 20% replacements of silica fume, fly ash, and metakaolin. Results obtained from adiabatic calorimetry and isothermal calorimetry testing showed that the concrete with SL had somewhat higher maximum temperature rise and heat release compared to other materials, regardless of SL replacement levels. However, there was a delay in time to reach maximum temperature with increasing SL replacement level. At 50 °C, a significant acceleration was observed for SL, which is more likely related to the pozzolanic reaction than the hydraulic reaction. Semi-adiabatic calorimetry did not show a greater temperature rise for the SL compared to other materials; the differences in results between semi-adiabatic and adiabatic calorimetry are important and should be noted. Based on these results, it is concluded that the use of blast furnace slag should be carefully considered if used for mass concrete applications.

Hydration Characteristics of Low-Heat Cement Substituted by Fly Ash and Limestone Powder

This study proposed a new binder as an alternative to conventional cement to reduce the heat of hydration in mass concrete elements. As a main cementitious material, low-heat cement (LHC) was considered, and then fly ash (FA), modified FA (MFA) by vibrator mill, and limestone powder (LP) were used as a partial replacement of LHC. The addition of FA delayed the induction period at the hydration heat curve and the maximum heat flow value (q_max) increased compared with the LHC based binder. As the proportion and fineness of the FA increased, the induction period of the hydration heat curve was extended, and the q_max increased. The hydration production of Ca(OH)₂ was independent of the addition of FA or MFA up to an age of 7 days, beyond which the amount of Ca(OH)₂ gradually decreased owing to their pozzolanic reaction. In the case of LP being used as a supplementary cementitious material, the induction period of the hydration heat curve was reduced by comparison with the case of LHC based binder, and monocarboaluminate was observed as a hydration product. The average pore size measured at an age of 28 days was smaller for LHC with FA or MFA than for 100% LHC.

The Effect of Specimen Size on the Results of Concrete Adiabatic Temperature Rise Test with Commercially Available Equipment

In this study, adiabatic temperature rise tests depending on binder type and adiabatic specimen volume were performed, and the maximum adiabatic temperature rises and the reaction factors for each mix proportion were analyzed and suggested. The results indicated that the early strength low heat blended cement mixture had the lowest maximum adiabatic temperature rise (Q_∞) and the ternary blended cement mixture had the lowest reaction factor (r). Also, Q and r varied depending on the adiabatic specimen volume even when the tests were conducted with a calorimeter, which satisfies the recommendations for adiabatic conditions. Test results show a correlation: the measurements from the 50 L specimens were consistently higher than those from the 6 L specimens. However, the Q_∞ and r values of the 30 L specimen were similar to those of the 50 L specimen. Based on the above correlation, the adiabatic temperature rise of the 50 L specimen could be predicted using the results of the 6 L and 30 L specimens. Therefore, it is thought that this correlation can be used for on-site concrete quality control and basic research.