Blended Mortars Research Articles

Pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing

Partial replacement of cement with high-volume slag reduces the amount of cement in concrete and thereby lessens the environmental pressure caused by cement production. This paper investigates the pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing, discusses the effects of slag content and pore structure on sulfate attack, and evaluates the methods for determining the sulfate resistance performance. The pore structure results show that the hydration of cement and/or slag reduces the porosity and most probable pore diameter (MPPD) and refines the pore structure of mortars. Steam curing primarily affects the pore size distribution but not the porosity for the mortars within 3 d. Increasing slag replacement increases the porosity for standard-cured and steam-cured mortars at the age of 28 d; however, it significantly reduces the air voids that are detrimental to sulfate resistance. Sulfate attack results show that the combination of the flexural strength test with the sulfate-ion content can evaluate the sulfate resistance well. The sulfate resistance improves with increasing slag content, and 70% of slag improves the sulfate resistance significantly for both standard-cured and steam-cured mortars. In addition, the MPPD, gel pores, and mesopores do not seem to determine the sulfate resistance. Reducing the volume fractions of large capillary pores, especially air voids, can improve sulfate resistance.

Recycling high volume Fe-rich fayalite slag in blended alkali-activated materials: Effect of ladle and blast furnace slags on the fresh and hardened state properties

The valorization of Fe-rich fayalite slag (FS) as a precursor for alkali-activated materials (AAMs) is hampered by its low reactivity at ambient temperature. Here, FS was blended with waste-based reactive co-binders such as ladle slag (LS) and blast furnace slag (BFS) to improve the fresh and hardened state properties of the AAMs for potential construction applications. The results showed that the incorporation of LS and BFS as an additional source of Ca and Al accelerated the reaction kinetics and influenced the binder gel type and formation mechanism. In all the mixes, Fe, Si and Na are present in the evolving binder gel. In addition to these elements, the binder gel of the blended formulations is also rich in higher quantities of Ca and Al and showed possible formation of C-A-S-H and C-(N)-A-S-H together with the development of andradite, a calcium ferrosilicate hydrate phase formed from chemical interaction between FS and co-binders; it indicates that both FS and co-binder participated in the binder gel formation. Furthermore, the nucleating and filling effects of co-binders improved the workability, ultrasonic pulse velocity and mechanical properties; this also densified the structure and lowered the water absorption and permeable porosity of the blended mortars. The compressive strength of blended mortars was above 20 MPa, thus satisfying the strength requirements of building materials according to ASTM C62. The results of this study emphasize the reuse potential of FS with other waste streams in producing eco-friendly AAMs, which can have a wide range of construction applications.

Non-Destructive Evaluation of Mortar with Ground Granulated Blast Furnace Slag Blended Cement Using Ultrasonic Pulse Velocity.

Non-destructive evaluation using ultrasonic pulse velocity (Vp) testing has extensive applications in the concrete industry. With advances in construction technology, the use of ground granulated blast furnace slag (GGBFS) as a partial replacement to cement in a concrete mix is growing in popularity primarily because it reduces the initial capital cost of raw materials and the associated energy costs. This paper investigates the effect of the water-to-cement (wc) ratio and the cement content replaced by GGBFS on the development with time of the ultimate compressive strength () and the compression wave velocity (Vp) of mortar. The results showed that in the case of mortar with higher percentages of GGBFS replacement (where nucleation surfaces are more abundant), increasing wc can increase but cause a decrease in Vp. The posterior hydration process is highly dependent upon the water particles in the mixture after the first stage of hydration. After 7 days of curing, experimental results show that the of slag blended cement mix design wc ratio of 0.6 surpassed the value of an Ordinary Portland cement. A regression model correlating the and Vp of slag blended mortar is developed, which can be used to predict at concrete ages ranging from 1 day to 28 days for mixes with GGBFS percentage replacement values ranging from 15% to 45%.

Strength and Microstructure of Coffee Silverskin Blended Mortar

This study pertains to incorporation of coffee silverskin (CSS) in partial replacement for ordinary Portland cement (OPC) in mortar, by investigating its fresh properties (setting and workability), compressive strength (3, 7, 14 and 28-day), absorption and microstructural characteristics. The objectives were to reduce environmental solid wastes and achieve cost efficiency in the use of construction materials. The CSS was expressed as a ratio of total binder (CSS/(OPC + CSS)) and varied from 0 to 5%. The findings revealed that CSS could reduce workability, setting time and early strength. It could also enhance the absorption of the CSS-blended mortar (CBM). The cause of reduction in workability was due to its contribution to the viscosity of the mixture due to the emulsification of the fat component (acetate) and aromatic compounds, as observed in the Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction techniques. The presence of these compounds also caused microstructural disintegration that resulted in the lower strength. In addition, the presence of other organic compound in CSS but absent in OPC enhanced microstructural disintegration and porosity in CBM. The 28-day strength of 25 MPa could be achieved in CSS-blended mortar if the CSS/(CSS + OPC) ratios were kept below 3%. The maximum compressive strength of 38.5 MPa was obtained with the optimum CSS content of 1 wt%. The relative density (water) of CSS was 0.345; therefore, it could also be used to produce lightweight concrete. This study promotes the valorization of raw CSS waste as construction material which could be used for subgrade in the construction of road pavement.

Hydration, Compressive Strength and Durability of Eco-friendly Cement Mortars Containing Recycled Brick Powder and Metakaolin

Grinding brick waste into powder for use as a supplementary cementitious material has shown to be a promising recycling method for the reuse of construction and demolition waste. However, the strength and durability of concrete containing recycled brick powder (RBP) will significantly decrease due to the poor pozzolanic activity of RBP, limiting its wider applications. This study attempted to overcome these defects through metakaolin (MK) addition. The hydration, compressive strength, durability, and environmental impact of eco-friendly mortars containing RBP and MK were investigated. The results showed that MK promoted the early-stage hydration of cement, creating a suitable hydration environment for the hydration of RBP at a later age. As a result, the volume fractions of low-density calcium silicate hydrate (C-S-H) and high-density C-S-H increased according to the nanoindentation test results. In addition, the strength, chloride penetration resistance, and reinforcement bar corrosion resistance of the blended mortars obviously improved due to the synergistic effect of RBP and MK. Lastly, we achieved CO2 emissions that were 22.1–30.2% lower and energy consumption that was 21.4–27.0% lower by incorporating 20% RBP and 5–15% MK.

The Mechanical Properties of Mortar Blended with Steel-PVA Hybrid Fibers and CaCO3 Whiskers Under Freeze/Thaw Cycles Condition

The Mechanical Properties of Mortar Blended with Steel-PVA Hybrid Fibers and CaCO3 Whiskers Under Freeze/Thaw Cycles Condition

Sustainability development and performance evaluation of natural hydraulic lime mortar for restoration.

Many efforts have focused on the deterioration of historic buildings, and natural hydraulic lime mortar without admixture is less resistant to environmental agencies than a lime mortar with admixtures. A research study has been carried out to study the effect of carboxymethyl cellulose (CMC) and alccofine (AF) with the natural hydraulic lime mortars in improving the hydraulic properties, durability properties, and freeze-thaw resistance. The performance of lime mortars was evaluated with various additives. The experimental results indicated the combined effect of CMCs and AF in lime mortars' compression testing in different stages. In blended mortars, the early compressive strength was increased. Also, mixed mortar exhibits stronger freeze-thaw resistance with a long healing period. These findings indicate that AF and CMC combination played an essential role in lime mortar (LM) properties, which is generally advantageous for restoration and conservation purposes, especially in historic structures in cold regions.

Durability of Construction and Demolition Waste-Bearing Ternary Eco-Cements.

In recent years, the development of ternary cements has become a priority research line for obtaining cements with a lower carbon footprint, with the goal to contribute to achieve climate neutrality by 2050. This study compared ordinary Portland cement (OPC) durability to the performance of ternary cements bearing OPC plus 7% of a 2:1 binary blend of either calcareous (Hc) or siliceous (Hs) concrete waste fines and shatterproof glass. Durability was measured further to the existing legislation for testing concrete water absorption, effective porosity, pressurized water absorption and resistance to chlorides and CO2. The experimental findings showed that the 7% blended mortars performed better than the reference cement in terms of total and effective porosity, but they absorbed more pressurized water. They also exhibited lower CO2 resistance, particularly in the calcareous blend, likely due to its higher porosity. Including the binary blend of CDW enhanced chloride resistance with diffusion coefficients of 2.9 × 10−11 m2 s−1 (calcareous fines-glass, 7%Hc-G) and 1.5 × 10−11 m2 s−1 (siliceous fines-glass, 7%Hs-G) compared to the reference cement’s 4.3 × 10−11 m2 s−1. The siliceous fines-glass blend out-performed the calcareous blend in all the durability tests. As the mortars with and without CDW (construction and demolition waste) performed to similar standards overall, the former were deemed viable for the manufacture of future eco-efficient cements.

Hydration Behaviour and Characteristics of Binary Blended Metakaolin Cement Pastes

Cement production consume large amount of energy to form clinker and carbon dioxide (CO2) emitted into the atmosphere causing global warming. To mitigate this challenge, the use of Metakaolin (MK) as supplementary cementitious material cannot be over emphasized. This study evaluated the use of Metakaolin (MK) on hydration development of MK--PC blended cements and strength of Mortars. The MK with a Blaine fineness of 7883 cm2/g was used to replace Portland Cement (PC) at a level of 0, 5, 10, 15, 20, 25 and 30 % by mass of PC at a constant w/b ratio of 0.50 to prepare blended cements. Hydration development of blended cement and compressive strength of Mortars were investigated using chemically bond water and free-lime contents and strength tests respectively. X – Ray diffraction (XRD) and scanning electron Microscopy (SEM) techniques were also utilised in the analysis of Pozzolanic reaction and hydration products. Test results indicates that Water of consistency, setting times for the mixes increased with increase in MK contents, influence of MK on the chemically bond water and free Lime contents of the blended cements were due to its filler and dilution effects and Pozzolanic reaction. The cumulative non-evaporable water and free-lime contents increased by partial replacement of PC with MK due to PC hydration and Pozzolanic reaction. The tested Mortar prepared with blended cements with 30 % PC replacement with MK shows a retardation of strength development with a low value at early ages (7 days) and increased in growth at later ages (28 days). The compressive strength of tested mortar for 90 days curing age for the blended mortar is 31 N/mm2 close to that of control Mortar (35 N/mm2). The results obtained from XRD and SEM analysis indicated increase in Calcium Hydroxide (CH) consumption and Calcium Silicate hydrate (C-S-H) formation in blended cement pastes with curing time. The PC replacement with MK induced changes in Microstructures of blended cement paste and chemical composition of hydration products. These results are potentials for modelling the behaviour of MK-PC blended cements.

Characterisation and pore structure analysis of mortar incorporating valorised rice husk ash

Physical, chemical, and mineralogical characterisation of as-received rice husk ash (RHA) samples sourced from four rice-growing regions (North, South, East, and West) of India is presented. Valorised RHA was obtained through controlled combustion at two temperature ranges (600–700 °C and 650–700 °C) of husks from the North in an industry set up. Valorisation efficacy has been tested through comparative characterisation of the valorised RHAs with the as-received RHAs from the four regions. Blending of 15% valorised RHA (in the beneficiated state) by weight of cement had no adverse effect on compressive strength even though water–binder ratio of the blended mortar had to be increased by 14% to achieve flow of the control cement mortar. Compared with the control cement mortar, porosity of the mortar blended with the beneficiated RHA measured using mercury intrusion porosimetry (MIP) increased by up to 10% primarily due to an increase in the number of large mesopores (0.01–0.05 µm).

Microstructure of Portland cement blended with high dosage of sewage sludge ash activated by Na2SO4

Sewage sludge ash (SSA) used as a supplementary cementitious material is one of the effective methods for sewage sludge disposal. Because of the weak pozzolanic reactivity of SSA, the incorporation of high dosage of SSA results in a significant degradation for the properties of Portland cement (OPC). This greatly limits the utilization of SSA. In this study, Na2SO4 was used as an activator and its effect on the hydration and microstructure of Portland cement blended with high dosage of sewage sludge ash (50% and 60%) was investigated. The SSA-OPC blended mortars exhibit extremely low compressive strengths due to the poor pozzolanic activity of SSA and its inhibition effect on the hydration of the blended systems. The compressive strength of the blended mortars is significantly improved with the addition of Na2SO4. At early age, the hydration of C3S is accelerated by Na2SO4. Thus, the generation of C-S-H gels and Ca(OH)2 are promoted to strengthen the matrix. Besides, Na2SO4 enhances the reaction of C3A with SO42− and thus promotes the formation of AFt in the blended systems. At later age, the pozzolanic reaction of SSA with Ca(OH)2 in the blended systems is enhanced because the concentration of alkali of the pore solution is increased with the incorporation of Na2SO4. This promotes the precipitation of additional C-S-H gels to fill the space around SSA particles and results in a dense microstructure of the matrix. Moreover, the addition of Na2SO4 avoids the undersulfation of the blended systems, leading to a transformation of the aluminate products from hexagonal plate-shaped AFm crystals and short needle-like AFt crystals with high C/S ratios to long needle-like AFt crystals with extremely low C/S ratios. The formation and growth of the long needle-like AFt crystals effectively refine the pore structure and increase the compressive strength of the blended systems.

Experimental study on the properties of ternary blended geopolymer rich mortar

Experimental study on the properties of ternary blended geopolymer rich mortar

Assessment of properties of mortars modified with sugarcane bagasse ash processed by heating at different temperatures as cement replacement

Recently, sugarcane bagasse ash (SBA), generated in boilers after combustion of sugarcane bagasse for cogeneration has been basically accepted as a pozzolanic material. In this study, SBA, which was first sieved through the No. 100 sieve (SBA-s) before burning at 600 °C, 700 °C, 800 °C for 1 h as post-treatment (denoted as SBA-600, SBA-700, SBA-800) was sequentially used as a partial replacement for Portland cement (i.e. 5%, 10%, 15%, 20% by weight) in casting blended mortars. Performance in fresh and hardened states of these mixes were examined and compared to that of the cement mortar (cement: sand of 1:2.75 and water-to-cement ratio of 0.57). The results indicate that the SBA-systems required more mixing water than Portland cement; whereas, blended pastes with a part of re-burnt ash manifested an acceleration of setting time compared to that with SBA-s. In addition, mortars prepared with SBA-700 or SBA-800 at replacement rates of 5% and 10% for cement showed the lowest porosity, the best both of mechanical strength and durability (in terms of sulphate resistance, surface resistivity). SEM analysis verifies that a dense phase was observed for the matrix of blended mortars contained 5–10% SBA-700 or SBA-800.

Cement substitution by sludge-biomass gasification residue: Synergy with silica fume

The increasing volumes of sewage sludge and other wastes of biological origin force the use of downdraft gasifiers for waste utilization; however, thermal processes produce residues that need to be treated in an environmentally acceptable way. The object of the study is to evaluate the possible application of residue, derived from industrial sewage sludge-biomass gasification plants, with silica fume as a partial binder substitute in cement-based materials. At total cement replacement levels of 10 and 12%, the dosages of gasification residue and silica fume varied in the range of 2–6% and 6–10% by cement mass, respectively. The impact of synergy between silica fume and gasification residue on the hydration and microstructure development of cement paste was analysed using SEM-EDS, XRD, TGA and N2 sorption methods. The synergy of wastes was found to change the morphology and assemblage of hydration products and to accelerate the consumption of portlandite. N2 physisorption revealed that the synergy of both substitutes had a significant impact on the distribution of pores in the mesoporosity range up to 30 nm, representing small microcapillary pores. The synergistic impact of the substitutes on selected properties of cement mortars was determined after 7, 28 and 56 days. Compared with the reference, all blended mortars showed 5–40% higher mechanical strength and 25–50% lower water ingress during the entire hydration period. The compressive strength increased with the reduction in the residue-to-silica fume (R/SF) ratio, while the flexural strength and sorptivity were less dependent on the ratio. The results revealed that the total cement substitution level may be increased up to 12%, within 4–6% covered by gasification residue, without losing the mechanical strength and consequently, to reduce the resources of Portland cement and silica fume.

Performance of waste glass powder as a pozzolanic material in blended cement mortar

In this study, the pozzolanic activity of finely ground waste glass powder (WGP) used as a partial cement replacement in mortars was investigated, and the WGP particle size, WGP content, and curing age were selected for analysis. Tests to determine the fluidity, compressive strength, scanning electron microscopy (SEM), energy dispersive X–ray spectroscopy (EDS), X–ray diffraction (XRD), Thermo–gravimetry analysis (TGA), Differential thermal gravity (DTG) and Fourier transform infrared spectroscopy (FTIR) were performed on a blended mortar. The results showed that when the WGP particle size was 20–44 μm and the WGP content was 20%, the fluidity of the slurry was higher than that of the control group, and the slurry exhibits good cohesion and water retention performance. When the WGP particle size ranges were 74–150 μm and 44–74 μm, the compressive strength of the blended mortar was smaller than that of the control group for all curing days regardless of the WGP content. When the WGP particle size was 20–44 μm, the compressive strength was lower than that of the control group at 7 d of curing, whereas it was 3.5% and 9.6% higher than that of the control group at 28 d and 90 d curing, respectively, with a WGP content 20%. When the WGP particle size was 15–20 μm, the compressive strength did not significantly increase compared with when the WGP particle size was 20–44 μm for the same WGP content, but slightly decreased. SEM and EDS showed that when the WGP particle size was 20–44 µm and the WGP content was 20%, the hydration products in the microstructure of the cement slurry were abundant, whereas pore cracks were few. This was additionally confirmed by XRD and TGA–DTG results, thereby verifying the formation of the lowest content of calcium hydroxide (CH) and the highest content of calcium silicate gel in the blended mortar. Variations in the Si–O and Al–O bond intensities shown in the FTIR spectrum supported this conclusion. Furthermore, the TGA–DTG results showed that the increase in calcium silicate gel content from 28 d to 90 d was higher than that from 7 d to 28 d, and that the activity of the WGP was more significant in the later curing period.

Strength, electrical resistivity and sulfate attack resistance of blended mortars produced with agriculture waste ashes

The performance of blended mortar mixtures produced with partial replacement of cement with agriculture waste ashes of rice husk, sugarcane bagasse, corncob, and waste wood were evaluated in this investigation. Cement was replaced at 5, 10, and 15 wt% with each of agriculture waste ashes for manufacturing of blended mortars. Fresh mixture properties, compressive strength, electrical resistivity, and sulfate resistance of the mixtures were evaluated at 7, 28, 56, and 90 days of curing ages and compared with that of control mixture.Test results showed a significant improvement in the later age compressive strength, electrical resistivity and sulfate resistance of blended mortar mixtures. Considerable increase in the initial and final setting times of the blended mortar mixtures was noted. Increasing demand for the superplasticizer dosage to achieve the target flow level was recorded with increase in percent replacement of cement with the agriculture waste ashes. Blended mortar mixtures produced with rice husk ash as partial replacement of cement showed superior performance among the four types of mixtures. A replacement level of 10 wt% of cement with the agriculture waste ashes was observed to be the optimum to achieve enhanced strength and durability of the blended mortar mixtures.

Utilizing shale gas drilling cuttings as admixture in cement mortars: a case study in Fuling, Chongqing, China.

Huge amount of water-based drilling cuttings (WDC) is generated during the drilling and exploitation of shale gas. In this study, WDC powder was used as a replacement of cement at different mass fraction (0, 10%, 30%, and 50%) to prepare cement mortars. The mechanical properties, water absorption, and heavy metals leaching of the mortars were then investigated along with the corresponding microstructures. The results showed that a higher porosity was formed within the WDC-blended mortars. For instance, the porosity of the control specimen was 16.7%, while the porosity increased to 20.6%, 21.4%, and 25.0% for the mortars blended with 10%, 30%, and 50% WDC, respectively. Therefore, the mechanical properties of the mortars decreased and their water absorption increased with the increase of WDC replacement ratio. For example, the compressive strength of the mortars blended with 10% and 30% WDC decreased from 33.11MPa of the control specimen to 29.33MPa and 21.48MPa, respectively. Nevertheless, the blended mortars still satisfied the M20 strength grade according to the Chinese standard (JGJ/T 98-2010). The compressive strength of the mortar blended with 50% WDC was 11.33MPa and then satisfied the M10 strength grade. The leaching test indicated that the water quality of leachates from the mortars blended with lower than 30% WDC remained as Grade I according to the Chinese standard (GB 3838-2002); the water quality of leachate from the mortar blended with 50% WDC was classified as Grade III, which, however, would not cause a safety issue to the environment.

Enhanced early hydration and mechanical properties of cement-based materials with recycled concrete powder modified by nano-silica

In recent years, an ever-increasing amount researchers dedicated themselves to exploring the possibility of introducing recycled concrete powder (RCP) into concrete as a substitute for cement. To optimize the effect of RCP on cement-based materials, this paper uses nano-silica (NS) to learn the hydration and mechanical properties of cement-based materials with RCP. The results indicated that after adding NS into RCP-cement pastes, the setting time of cement pastes was significantly reduced, while the samples' early hydration rate and hydration heat increased. Besides, the mechanical strength of the mortar decreased as RCP replaced part of the cement, while 2% NS can compensate for the mechanical strength loss of mortar caused by RCP as supplementary cementing materials. The X-ray computer tomography (X-ray CT) and mercury intrusion porosimetry (MIP) results showed that RCP increased mortar's pore volume fraction and porosity. In contrast, NS in RCP blended mortar significantly decreased the number of pores with a pore volume between 0.01 and 0.03 mm3 and increased the proportion of harmless pores (From 28.6% to 31.4%). Hence, NS reduced the pore volume fraction and porosity of mortar. The results of X-ray CT and MIP showed that NS could refine the pore size in RCP blended mortar. X-ray diffraction (XRD) and scanning electron microscope (SEM) further revealed that the existence of NS can eliminate the adverse effects brought by RCP.

Pozzolanic reactivity of aluminum-rich sewage sludge ash: Influence of calcination process and effect of calcination products on cement hydration

The application of aluminum-based flocculant in wastewater treatment results in a large amount of aluminum-rich sewage sludge. This work investigated the influence of calcination process on physicochemical characteristics and pozzolanic activity of aluminum (Al)-rich sludge ash and studied the effect of sludge ash on cement hydration. The results showed that higher calcination temperature from 600 ℃ to 900 ℃ increased the amorphous content in sludge ash. The pozzolanic activity of sludge ash calcined at 800 ℃ and 900 ℃ was confirmed by Frattini test. In view of strength activity index of blended mortar and energy conservation, the optimal calcination condition of sewage sludge ash was calcined at 800 ℃ with air-cooling. The addition of sludge ash promoted the transformation of ettringite to monosulfate phase in cement paste. However, the high Al concentration dissolved from S6 and S7 ash inhibited significantly the cement hydration and resulted in low compressive strength values of the blended mortars. The pozzolanic reaction of S8 and S9 ash produced more hydration heat and additional Al-bearing products such as katoite and monosulfate which contributed to the strength development of mortars. Furthermore, the heavy metals in sewage sludge can be immobilized in ash structure during calcination process and the structure of hydration products, which ensures the environmental security of sludge ash utilization in construction materials.

High strength fiber reinforced one-part alkali activated slag composites from industrial side streams

This paper details the effect of fiber reinforcement on mechanical characteristics of by-products based one-part alkali activated material (AAM). Two different binder matrices were considered in this study, such as, plain slag, and ternary blended slag, to understand their efficiency in fiber reinforced system. These matrices were reinforced with 1% v/v of three different fibers (steel, glass and basalt) to improve the flexural performance of high strength mortar blends. Steel fiber reinforced one-part AAM outperforms mineral fibers in compressive strength contribution. The fracture energy of steel fiber reinforced compositions was roughly 4 times higher than that of mineral fiber reinforced materials. In addition, the flexural performance of ternary blended matrix was higher than that of slag-based composition regardless fiber types and properties. Finally, preliminary finite element modelling was considered to assess the applicability of the concrete damage plasticity constitutive model in predicting the nonlinear behavior of the developed composites. The numerical predictions proved the accuracy of the model with good agreement between experimental and numerical results.