Blended Cement Mortars Research Articles

Physical and mechanical properties of pozzolanic materials blended cement mortars before and after the freeze-thaw cycles

Today, Portland cement (PC) production causes a significant release of carbon dioxide (CO2) gas into the atmosphere. The CO2 gases released into the atmosphere create environmental pollution worldwide and prevent current and future generations from living in a cleaner nature. One of the most effective ways of restricting PC use in concrete mixes is to use different types of industrial wastes by replacing them with PC. Using industrial wastes such as fly ash (FA), SF, and MP in concrete mixtures by replacing cement in specific proportions is vital in terms of sustainability. The primary purpose of this study is to examine comparatively the effects of fly ash (FA), silica fume (SF), and marble powder (MP) replaced with cement at the rate of 10%, 20%, and 30% on the flowability, mass loss, and residual compressive strength (RCS) of mortars before and after F-T cycles. According to the results, the effects of FA, SF, and MP on mortars' fresh and hardened properties vary considerably. However, using FA, SF, and MP instead of cement significantly improves the matrix's weak cement/aggregate interface transition zones (ITZ) by showing the filler effect. They contribute considerably to reducing mass losses and increasing the RCS capacities of mortars. Compared to room conditions, the reduction in RCS capacities of the control mortar was 21.32% after 200 F-T cycles, while the decrease in RCS capacities of FA-, SD-, and MP-added mortars was between 7.86 and 19.85%. While the mass loss of the control sample after the 200 F-T cycle is 1.23%, the mass loss of mortars with FA, SF, and MP additives is lower and varies between 0.44% and 1.02%.

Comparative effects of different real conditions in the microstructure and properties of ternary blended cement mortars for being used in rehabilitation works

The use of ternary binders in commercial cements is very low, at least in Spain. A possible field of application of these ternary cements would be the rehabilitation of coatings of old buildings, whose performance may be affected by the external environment. The goal of this research is to analyze the comparative effects of two in-situ environments in the microstructure and several service parameters of mortars with several ternary binders. The real environments verified the requirements of classes XC3 and XC4 of Eurocode 2. The mortars were also exposed to an optimum condition. Reference mortars with ordinary Portland cement and binary mortars were also studied. Mercury intrusion porosimetry, carbonation depth measurements and mechanical strength tests were performed. The real in-situ environments produced a carbonation development, an overall lower pore refinement and worsening of mechanical properties. Mortars which incorporated at least one active addition generally presented a better performance.

Potential utilization of regional cashew nutshell ash wastes as a cementitious replacement on the performance and environmental impact of eco-friendly mortar

Globally, agro-waste ashes are increasing significantly due to the rapid implementation of biomass-based power plants. In the present trend, agro-wastes are disposed of in an unsustainable manner. The recycling of agro-waste has significantly contributed to sustainable goals. In the construction sector, it is possible to dispose of waste more efficiently. However, the efficiency of locally available agro-residual waste in cementitious composites is not well understood. In the present investigation, the practicability of using agro-residual ash obtained from the burning of cashew nutshells on the properties of eco-friendly blended cement paste and mortars is explored. Blended cement mixtures containing cashew nutshell ash (CNSA) were prepared at five replacement levels, 5, 10, 15, 20, and 25%, relative to the weight of the cement. To understand the characteristics of CNSA, microstructure investigations such as X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy, and energy-dispersive spectroscopy analyses were performed. Paste properties of CNSA-based cement are observed through consistency, setting time, mini-slump flow, and expansion tests. For the CNSA-based mortars flow table, compressive strength, ultrasonic pulse velocity (UPV), electrical resistivity (ER), water absorption, bulk density, and porosity tests were performed to understand its efficiency. The strength indices of mortars were used to quantify the pozzolanic effect of CNSA. With the incorporation of CNSA, water demand increased by 57%, initial and final setting time decreased by 90% and 83%, respectively. Results showed that CNSA-based mortars absorbed more water and had higher porosity, which reduced compressive strength, UPV, and ER values. CNSA blended mortar is more suitable for applications that do not require high compressive strength. Results indicated that the compressive strength, UPV, and ER are within the limit specified. Strength indices indicated that CNSA has a positive and negative pozzolanic effect during early and later ages, respectively. Further, the sustainable assessment showed that the introduction of CNSA in mortar could substantially reduce embodied carbon, embodied energy, and strength efficiency over the control mortar. The inadequate amount of SiO2, Fe2O3, and Al2O3 in CNSA makes it an unsuitable pozzolanic material. However, it can be utilized in smaller amounts as a fractional replacement of cement and is found to be promising for specific desired properties of cement as a cost-effective accelerator.

The comparative study of using wood ash in lieu of fly ash in South African blended cement paste and mortar

A comparative analysis of the properties of fly ash (FA) and wood ash (WA) blended cement, produced in the controlled environment of a cement factory was examined. Since FA has been adopted in South Africa as a material for blended cement, the possibility of using wood ash in lieu of FA to produce blended cement was investigated. The blended cements were prepared and tested at AfriSam (South Africa) Ltd. Roodepoort, with 10 % and 25 % FA and WA as partial substitution for Ordinary Portland Cement (OPC) clinker (CEM1). The chemical composition of FA and WA, the setting times of the blended cement pastes and the compressive strengths of the blended cement mortars were analyzed and discussed. The results indicated that FA and WA have combined SiO2, Al2O3 and Fe2O3 constituents of 89.29% and 72. 58%, respectively. Also, lower initial and final setting times were observed with 25% WA samples as compared to the control sample and FA samples. WA blended cement showed faster rate of hydration than FA blended cement at early curing age resulting in mortar compressive strength of 26.2 MPa and 25.4 MPa as well as 22.6 MPa and 19.2 MPa for 10% and 25% WA and FA substitution respectively. However, FA blended cement mortar exhibited higher late strength than WA blended cement mortar with 10% FA blended cement mortar resulted in higher compressive strength than control sample at 90 days. The combined synergy of WA and FA in blended cement is envisaged to produce mortar of desirable early and late strengths.

Application of pyrophyllite in high-temperature treated building materials

Phyllosilicate mineral pyrophyllite is predominantly used in the ceramic industry because it exhibits high refractoriness. Due to its thermal transformation into mullite, pyrophyllite is stable at elevated temperatures, making it a suitable mineral additive for refractory non-shaped materials and various ceramic shaped products. In this study, pyrophyllite is employed as 50 % clay replacement in the ceramics and up to 30 % cement replacement in mortars. Physico-mechanical properties were investigated. The firing shrinkage in the ceramics treated at 1200 ?C was reduced by pyrophyllite addition. Pyrophyllite acted as additional pozzolana during cement hydration. Within the microstructure, it formed micro-reinforcement in the shape of crystalline folia, which improves the mechanical properties of ordinary Portland cement, high aluminate cement, and blended cement mortars. The investigation proved the efficiency and suitability of pyrophyllite employed as a substitution for clay in ceramics and a cement replacement in mortars.

Evaluation of pozzolanic activity of ternary blended supplementary cementitious material with rice husk ash and GGBS

The utilization of industrial and agricultural waste materials as supplementary cementitious material in blended cements provides an adequate solution for reducing the greenhouse emission and the environment concerns associated with waste management. Few literatures have been reported on the partial substitution of cement with the blended usage of mineral admixtures such as GGBS and RHA in cement mortars. The effect of blended usage of the mineral admixture as partial replacement of cement are investigated based on the physical and pozzolanic properties of ternary blended cement mortar. An optimal proportion of RHA -GGBS blended supplementary cementitious material is proposed based on strength activity index for utilizing them in ternary blended cement. The blended supplementary cementitious material with 30% rice husk ash and 70% ground granulated blast furnace slag as constituent materials are identified as the optimal proportion for achieving better pozzolanic activity.

Performance of blended cement mortar modified with fly ash and copper slag

Performance of blended cement mortar modified with fly ash and copper slag

Enhancing the Pozzolanic Reactivity of Spent Bleaching Earth Ash (SBEA) in Binary Blended Cement Mortar through Calcination

The effects of calcination on spent bleaching earth ash (SBEA) were investigated in terms of its contribution to pozzolanic reactivity as well as the strength of blended cement mortar when used as partial cement substitution. SBEA waste, which is plentiful in the global stock, showed some potential as pozzolanic material to reduce reliance on the traditional clinker cement. However, actual research on its use as cement replacement and how it may benefit from calcination was still very limited. This paper can conclude that SBEA contains sufficient silica and alumina oxides as well as satisfactory levels of pozzolanic reactivity to be classified Class N natural pozzolan. By calcining SBEA up to a temperature of 700 °C, its pozzolanic reactivity was improved due to the amorphisation of its contents, leading to an increase in the allowable level of replacements from 30 to 40 % as well as the peak strength achieved. These findings allowed calcined SBEA to be used in greater volume in cement mortar compared to an untreated SBEA. It is also worth noting that an excessively high calcination temperature around 900 °C was found to be detrimental to both the pozzolanic reactivity and strength development of cement mortars.

Effects of carbonation degree of semi-dry carbonated converter steel slag on the performance of blended cement mortar – Reactivity, hydration, and strength

Converter steel slag is the main by-product of steel making process. Around 150–250 million tons of steel slag can be produced in worldwide annually. The high-end application of converter steel slag in cement-based building materials is still facing the challenge due to its poor reactivity. In this study, semi-dry carbonation treatment of converter steel slag powder was investigated to improve the reactivity of slag powder and to sequestrate CO2. The properties of semi-dry carbonated converter steel slags were characterized and the performance of blended cement mortars were evaluated. The results exhibited that the semi-dry carbonation process of converter steel slag was slow, the carbonation degree of it reached 58.95% after 72 h’ treatment. In the pozzolanic reactivity test, the highest calcium hydroxide consumption ratio of carbonated converter steel slag achieved 30% compared to the reference (quartz) with a carbonation degree of 58.95%. However, the pozzolanic reactivity of carbonated converter steel slag cannot reflect the reactivity in blended cement systems. A retardation effect on the hydration process was observed in blended cement pastes with medium (43.76%) and high (58.95%) carbonated converter steel slag powder due to the presence of the high amount of vanadium leached from carbonated converter steel slag particles (10.653 mg/L and 18.831 mg/L). A medium carbonation degree (43.76%) of converter steel slag was observed to induce the largest amount of calcium silicate hydrates and highest compressive strength of cement blends compared to slag powder with low (33.35%) and high (58.95%) carbonation degree.

The Early Age Hydration Products and Mechanical Properties of Cement Paste Containing GBFS under Steam Curing Condition

The hydration products and strength of cement pastes incorporated with ground blast furnace slag (GBFS) (0% and 20% replacement) have been investigated under steam curing condition (80 °C for 7 h and 7 d) in comparison with normal curing condition (moist curing for 28 d). The results show that, during the initial 80 °C steam curing for 7 h, in addition to the filler effect, GBFS is still involved in cement hydration. The abundant available Al phase and Mg phase in GBFS promote the formation of flake-like hydrotalcite, foil-like C-(A)-S-H gels, as well as equant grain-shaped C-(A)-S-H gels. Prolonging the steam curing time to 7 d further improves the formation of hydrogarnet. Since the formation of both hydrogarnet and hydrotalcite can consume the available Al, steam curing for 7 d seems to favor the formation of low Al C-(A)-S-H gels. In addition, due to the formation of a large amount of hydration products, the influence of 20% GBFS addition on the demolding strength of initial steam-cured cement mortar (80 °C for 7 h) is almost negligible. However, further extending the steam curing time to 7 d increases the strength gap between 20% GBFS blended cement mortar and pure cement mortar, and the related mechanism is discussed.

Effect of curing temperature on the early and later ages behaviour of Metakaolin blended cement mortars: hydration heat and compressive strength

ABSTRACT Cement is one of the main sources of negative environmental impact of concrete. One way to reduce this impact of concrete could be through the reduction of the cement content. This could be achieved by replacing a part of cement with mineral additives such as fly ash, blast-furnace slag, silica fume, metakaolin (MK), etc. in concrete. In this paper, the effect of curing temperature on MK blended cements is investigated. Isothermal calorimetry and compressive strength tests are performed on mortars prepared with various replacement levels of cement by MK (5%, 15% and 25%) and cured at different temperatures (10°C, 20°C and 40°C). Further, water porosity test and microscopic observations were carried out to confirm the findings. Results showed that the pozzolanic activity of MK is conditioned by the curing temperature and its levels of replacement.

Mitigation effect of accelerators on the lead–zinc tailing induced retardation in autoclaved concrete

• Na 2 CO 3 significantly shortens the induction period of lead–zinc tailing cement pastes. • Na 2 CO 3 promotes the alkali activation of SiO 2 in tailing under autoclave curing. • No apparent coating of zinc containing compounds can be seen on C 3 S surface. • Accelerators inhibit the retardation by promoting the dissolution of cement particles. Reutilization of lead–zinc tailing in autoclaved concrete greatly reduces the land pollution by the wastes and CO 2 emission by the cement production. Given the retardation of lead and zinc on the cement hydration, three kinds of accelerators, Na 2 CO 3 , Li 2 CO 3 and triethanolamine (TEA) were employed. In this paper, the effect of accelerators on the autoclaved lead–zinc tailing blended cement mortars was investigated from aspects of compressive strength, hydration heat, phase assemblages and leachability of cement mortar. Results show that when the dosage of lead–zinc tailing exceeds 20 %, the demolding strength and the autoclaved strength of cement mortar decrease with increasing tailing dosage. Compared with Li 2 CO 3 and TEA, Na 2 CO 3 shows a more effective accelerating impact on the cement hydration. Incorporating 0.5 % Na 2 CO 3 can shorten the induction period of the lead–zinc tailing cement pastes by 20 h. Additionally, the SiO 2 in lead–zinc tailing can react with cement under autoclave curing, and the reaction is obviously promoted by the incorporation of Na 2 CO 3 . It lies in that Na 2 CO 3 and Li 2 CO 3 inhibit the retardation of lead–zinc tailing by promoting the dissolution of cement and nucleation of hydrates.

A bio-inspired, plant-derived admixture for metakaolin blended cement mortars

Partially replacing ordinary Portland cement (OPC) with metakaolin (MK) can refine the pore structure, improve mechanical properties, and enhance the durability of concretes. However, MK tends to agglomerate due to its high surface area and high concentration of hydroxyl groups. To overcome this problem, this study exploits a plant-derived polyphenol, tannic acid (TA), as an eco-friendly admixture to disperse MK. Due to its similar chemical functional groups as the adhesive protein in the mussel byssus, TA can adhere to various surfaces like the mussel’s adhesive protein. An experimental program was carried out to characterize the TA treated MK and investigate the effects of the proposed method on the properties of the cement paste and mortar. After mixing with the MK, TA can be adsorbed on the surface of MK particles, achieving deflocculation and dispersion of mineral grains by electrostatic repulsion forces and steric effect, significantly improving the workability of the mortar. Pore structure analysis suggests that TA dispersion densifies the hydration products, as revealed by the much-reduced gel and interhydrate pores. The nanoindentation results indicated that all low-density calcium hydrate silicate (CSH) was converted to high density by the TA dispersion, leading to a drastic improvement in the compressive strength of the produced mortars. As a result, the 28 days compressive strength of cement mortar prepared with TA dispersed MK was enhanced by up to 97 % compared with the one prepared without MK substitution, which exhibits great potential in reducing the carbon footprint of cement-based construction materials.

Potential of Calcined Brick Clay as a Partial Substitution in Blended Cement Mortars

Potential of Calcined Brick Clay as a Partial Substitution in Blended Cement Mortars

Bio-Based Admixture (Black Tea Extraction) for Better Performance of Metakaolin Blended Cement Mortars.

With high pozzolanic reactivity, metakaolin (MK) is a popular supplementary cementitious material (SCM), which can be used to partially replace Portland cement in concretes. Due to its small particle size, however, MK can agglomerate, resulting in a nonuniform matrix and underperformance of the produced concrete. To address this issue, this paper exploits a low-cost, bio-based admixture—black tea extract (BTE)—to replace the traditional petroleum-based chemical admixture to enhance the dispersion and workability of MK blended cement mortars. Major biomolecules in the BTE such as caffeine, catechin, theanine, and theaflavin are rich in polyphenol, hydroxyl, and carboxylic acid groups, which can interact with cement particles and have profound effects on the hydration process and microstructure of the hydration products. Experimental studies showed that BTE does improve the workability of the MK blended cement mortar. More importantly, the BTE introduces significant change on the microstructure of the hardened pastes. Both the pores with size less than 50 nm and the total porosity of the hardened paste were significantly reduced, leading to a significant improvement in the micro- and macro-mechanical properties of the hardened paste. Experimental results suggest that up to 35% greater improvement in the compressive strength at 28 days was achieved using the proposed bio-admixture. Economic and environmental advantages of using the BTE as a renewable admixture were also illustrated through analyzing the cost–benefit, embodied carbon, and eco-efficiency of the MK blended mortars.

Effect of Calcite on Fresh and Hardened Properties of Expanded Perlite Blended Cement Mortars

Expanded perlite, which is mostly used for purposes such as lightweight concrete and insulation, contains a high percentage of silica and alumina. Problems in early-term strength development occur with the high-volume substitution of normal weight and lightweight pozzolanic materials in the production of cement. It was thought that it would be important to examine the early period fresh and hardened properties of expanded perlite blended cement including nano and micronized calcite minerals with high reactivity and high specific surface area/volume ratio. For this purpose, a total of nine different mortar mixtures containing 0%, 6% and 18% expanded perlite and 5% nano and micronized calcite were designed for replacing by cement. For mortar samples modified with nano and micronized calcite and containing expanded perlite at different rates; mini slump flow test, standard consistency, setting times and soundness (Le Chatelier Method) tests/analyses were performed as fresh and early period properties. In addition to this, compressive strength and ultrasound pulse velocity tests were performed for the curing ages of 7, 28 and 120 days as hardened properties. Experimental results showed that expanded perlite negatively affects the early and hardened properties of mortars, and in general, improvements are achieved with nano/micronized calcite substitution. 23.2% and 45.4% of strength development has been achieved in the mixture including both calcite and expanded perlite within the curing ages of 7-28 days and 7-120 days, respectively. Also, a maximum of 5.7% of reduction was observed in EP blended cement mortars, including 18% of EP. Since nano-sized calcite has a higher surface area compared to micronized calcite, better contributions to the fresh and hardened properties were observed in the utilisation of nano-sized calcite.

A comparative physio-chemical study of steel slag blended cementitious materials in presence of hydroxyethyl methyl cellulose

The applications of steel slag (SS) in the cement industry provide a sustainable solution both for construction materials and industrial solid wastes, but the problem of easily bleeding presents a threat to its later performance and utilization efficiency. This work was designed to improve the water retention of SS blended cement by using hydroxyethyl methyl cellulose (HEMC) and evaluate the physio-chemical properties of the modified SS cement. The interaction mechanism between HEMC and SS blended cement was explored via calorimetry, acoustic and electroacoustic spectrometer, low-field NMR relaxometry, XRD, TG-DSC, as well as fluorescent microscopy. Results show that the water retention of SS blended cement mortar is improved both by ultra-fine grinding and incorporating HEMC, while the water retention rates are prominently increased from 84.87% to 94.35% by 0.1% HEMC. Ultra-fine grinding is able to activate SS and improve water retention ability more efficient compared with the application of HEMC. HEMC does not modify the amount of hydration heat but postpones the occurrence of the exothermic peak. A sudden increase in zeta potential demonstrates the Ca2+-adsorption on surfaces of SCM and cement particles. An additional peak commences on the 1H NMR spectrum of HEMC incorporated cement paste, which reflects the water adsorbed by HEMC, starting to submerge after 500 min via the desorption of water. HEMC affects the SS blended mortar via adsorbing on particles in the paste, capturing water and Ca2+ around it, thus improving the water retention and retarding the hydrate-polymerization.

Hydration and Mechanical Properties of Blended Cement with Copper Slag Pretreated by Thermochemical Modification.

The application of granulated copper slag (GCS) to partially replace cement is limited due to its low pozzolanic activity. In this paper, reconstituted granulated copper slag (RGCS) was obtained by adding alumina oxide (Al2O3) to liquid copper slag. Blended cement pastes were formulated by a partial substitute for ordinary Portland cement (OPC) with the RGCS (30 wt%). The pozzolanic activity, mechanical development, and the microstructure were characterized. The results show that 5–10 wt% Al2O3 contributes to the increase in magnetite precipitation in RGCS. The addition of Al2O3 alleviates the inhibition of C3S by RGCS and accelerates the dissociation of RGCS active molecules, thus increasing the exothermic rate and cumulative heat release of the blended cement pastes, which are the highest in the CSA10 paste with the highest Al2O3 content (10 wt%) in RGCS. The unconfined compressive strength (UCS) values of blended cement mortar with 10 wt% Al2O3 added to RGCS reach 27.3, 47.4, and 51.3 MPa after curing for 7, 28 and 90 d, respectively, which are the highest than other blended cement mortars, and even exceed that of OPC mortar at 90 d of curing. The pozzolanic activity of RGCS is enhanced with the increase in Al2O3 addition, as evidenced by more portlandite being consumed in the CSA10 paste, forming more C-S-H (II) gel with a higher Ca/Si ratio, and a more compact microstructure with fewer pores than other pastes. This work provided a novel, feasible, and clean way to enhance the pozzolanic activity of GCS when it was used as a supplementary cementitious material.

Response surface methodology for the optimization of CO2 uptake using waste concrete powder

The novelty of this study is to find out the CO2 uptake of waste concrete powder (WCP) derived from construction and demolition (C&D) waste recycling plant. The CO2 uptake of WCP was determined by the response surface methodology (RSM) considering the influence of carbonation time (t) and water-to-solid (w/s) ratio so as to realize the optimal condition to maximize the CO2 uptake via mineral carbonation of WCP. A regression model was developed and validated with experiments for the optimization of CO2 uptake. The response surface plot and analysis of variance show that increase in carbonation time increased the WCP CO2 uptake irrespective of w/s ratios. At carbonation time of 90 h and 0.4 w/s ratio, the optimum CO2 uptake was 2.81% considering the carbonation and energy efficiencies. The physio-chemical changes in WCP after carbonation were characterized together with heavy metal leaching performance. The blended cement mortar with carbonated WCP has a strength activity index of more than 75, which proves the feasibility of applying WCP as supplementary cementitious material for CO2 sequestration.

The engineering properties and pozzolanic reaction kinetics of quaternary blended binder high strength mortars optimized by the Taguchi method

The Taguchi method has been applied for the experimental design of the mixture proportions of quaternary blended cement mortars on the basis of four factors. The design of experiment derived mixture proportions have been examined on four levels, comprising supplementary cementitious materials (SCMs) viz: ultra-fine treated palm oil fuel ash (u-TPOFA; at 4 levels of 30, 35, 40, and 45%), ground granulated blast furnace slag (GGBFS; at 4 levels of 12.5, 15, 17.5, and 20%), metakaolin (MK; at 4 levels of 7.5, 10, 12.5, and 15%) as partial replacement of ordinary Portland cement (OPC), and water to binder ratio (W/B; at 4 levels of 25, 26, 27, and 28%), in order to achieve an optimum mixture. The response factors employed were compressive strength (CS), porosity (P%), and water absorption (Abs%) at the ages of 3, 7, 14, and 28 days. By utilizing the L16 array as proposed by the Taguchi method, the specimens prepared were analyzed using 16 experiments. The results obtained showed that the response values of the optimized mixture using the Taguchi method were much better than the plain cement mortar mix and those proposed in the initial 16 series. The workability of the optimum mix increased by about 6% over the plain cement mortar mix. The relative CS results of the optimum mix was 116.92% at 28 days of curing. Likewise, the relative P% and Abs% results of the optimum mix exhibited notable reductions at 28 days of about 40.0% and 45%, respectively. Further analyses were carried out using thermogravimetric (TG) and x-ray diffraction (XRD) analyses to quantify the contribution of the SCMs and their chemical reaction which was reflected by the remaining amount of the unreacted portlandite in the mix. According to the results, the optimum quaternary blended binders mortar mix which utilized only 37.5% of cement by volume (i.e., a reduction from 882.22 to 330.83 kg/m3) portrayed improved physical properties, chemical reaction, enhanced workability, better CS, as well as lower P% and Abs% compared to the plain cement mortar.