Showing papers on "Mortar published in 2022"

Characterization of sustainable mortar containing high-quality recycled manufactured sand crushed from recycled coarse aggregate

Abstract: The current utilization of low-quality recycled fine aggregate sourced from concrete waste acting as river sand replacement cannot achieve the preparation required for high-quality recycled mortar, due to abundant existence of hardened old mortar in recycled fine aggregate. In this work, an innovative and viable approach is proposed to crush recycled coarse aggregate into recycled manufactured sand, which has high-quality properties similar to the manufactured sand crushed from natural stone, for preparing high-quality recycled mortar with high strength and good durability. The results showed that recycled manufactured sand constituted by large proportion of natural stone particles and small proportion of old mortar, owned higher apparent density and lower water absorption than recycled fine aggregate. Incorporating recycled fine aggregate increased the drying shrinkage and decreased the mechanical strength; however, the substitution of natural river sand by recycled manufactured sand in mortar decreased the drying shrinkage as a result of its irregular shape and coarse surface, meanwhile, first increased and then declined the mechanical strength following the increase of the replacing percentage, amongst which the mortar containing 50% recycled manufactured sand showed the best mechanical strength. The tested mortars with recycled manufactured sand showed a general increment in the water and chloride ingress yet exhibited the water absorption and chloride ingress much lower than the mortar with recycled fine aggregate. Particularly, decreasing the content of hardened old mortar in recycled manufactured sand further improved the properties of recycled mortar.

High-temperature behavior of polyvinyl alcohol fiber-reinforced metakaolin/fly ash-based geopolymer mortar

Abstract: Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar is an eco-friendly construction material with excellent mechanical properties and durability. Visual observation, mass loss measurement, cubic and prism compressive tests , flexural tests, thermogravimetric and differential thermal analysis , scanning electron microscopy, and bubble parameter tests were conducted to evaluate the effect of PVA fiber and exposure temperature on the behavior of PVA fiber-reinforced geopolymer mortar after exposure to high temperatures. The PVA fiber contents were selected as 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%, and the target temperatures were 25 °C, 200 °C, 400 °C, 600 °C and 800 °C. The results indicate that significant mass loss of the geopolymer mortar could be observed when the exposure temperature increased from 25 °C to 250 °C, whereas slight mass loss occurred from 250 °C to 700 °C, and no mass loss was detected from 700 °C to 800 °C. As the temperature increased, the geopolymer mortar gradually densified, while the geopolymer mortar continuously developed more cracks and pores. The compressive and flexural strengths of the geopolymer mortar improved as the temperature increased from 25 °C to 200 °C, but it decreased significantly as the temperature further increased to 800 °C. In addition, on exposure to 200 °C, the presence of PVA fibers significantly improved the cubic and prism compressive strengths and flexural strength by 50.5%, 29.4%, and 66.3%, respectively, compared with the geopolymer mortar without fibers. As the temperature increased above 200 °C, although the PVA fiber decomposed, the defects left by the melt fibers slightly influenced the strength of the geopolymer mortar.

Basalt Fibers in Modified Whisker Reinforced Cementitious Composites

Abstract: The calcium carbonate whisker (CW) and basalt fiber are gaining popularity due to its enhanced mechanical properties in composites. Also, the short and long fibers provide bridging role and resistance against cracking from micro- to macro-scale, respectively. The usage of long and short hybrid basalt fiber along with addition of CW in cement-based composites is still a research gap. In this work, experimental behavior of CW basalt hybrid fiber reinforced mortar is considered with various content and length (3 mm, 6 mm, 12 mm, and 20 mm) of hybrid basalt fibers. In addition to this, synergy performance index is determined to quantitatively evaluate the positive interaction of hybrid basalt fiber in cementitious materials. The strengthening effect of whiskers and basalt fibers are also studied using scanning electron microscopy. The CW with various basalt fiber contents having different length of hybrid basalt fiber is used. It was found that the four various length of hybrid basalt fiber together with CW in cement mortar exhibited enhanced compressive, flexural, and split tensile strength than that of pure mortar and single length basalt fiber reinforced cementitious mortar. The results of synergy performance index showed similar trend with the experimental results. The strengthening effect caused by step by step crack arresting mechanism was also observed in cementitious material.

Performance of Self-Compacting Mortars Modified with Nanoparticles: A Systematic Review and Modeling

Abstract: During the transition of one material from macro- to nano-range size, considerable changes occur in the electron conductivity, optical absorption, mechanical properties, chemical reacting activity, and surface morphology. These changes can be advantageous in the production of new mixture composites. Due to the need for developing improved infrastructure, new and high-performance materials should also be developed. In this regard, to improve the performance of concrete mixtures, several methods have been investigated, including using nanoparticles (NPs) to enhance various characteristics of the concrete composite like improving fresh and mechanical properties of self-compacting concrete (SCC) as well as improving permeability and absorption capacity of the composite by providing extremely fine particles to fill micro-pores and voids. In this paper, a state-of-the-art review was carried out on the influence of various NPs inclusion on the fresh, mechanical, and durability properties of self-compacting mortars (SCM). So that current and most recent studies previously published were investigated to highlight the influences of different NPs on the slump flow diameter, V-funnel flow time, compression and flexural strengths, water absorption, chloride penetration, and electrical resistivity. Moreover, the main section of this study was devoted to proposing different models, including nonlinear model (NLR), multi-logistic model (MLR), and artificial neural network (ANN), to predict the compressive strength (CS) of SCMs modified with NPs. Based on the analyzed data, it was illustrated that the addition of NPs into SCMs significantly enhances the fresh, mechanical, and durability performance of SCMs. Moreover, the microstructure of SCMs was considerably improved due to the higher specific surface area of NPs and their reaction with undesirable C–H which present in the cement paste matrix to produce additional C-S-H gel.

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

Abstract: 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.

Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests

Abstract: Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens. The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.

Influence of carbonation treatment on the properties of multiple interface transition zones and recycled aggregate concrete

Abstract: Because of the carbonation treatment of recycled coarse aggregates (RCAs), the properties of the weak multiple interface transition zones (ITZs) in recycled aggregate concrete (RAC) can be improved, contributing to the enhanced behaviour of the RAC. In this study, different carbonation conditions (carbonation pressure, initial moisture contents of the RCAs and carbonation duration) were considered. A model of the RACs (MIRAC) was prepared to accurately locate multiple ITZs. Nanoindentation tests , scanning electron microscopy (SEM) tests were conducted to study the effect of carbonation treatment on the microproperties of RAC. At the same time, the influence of the carbonation treatment on the compressive strength and chloride ion penetration resistance of the RAC was evaluated. Moreover, the relationship between the microproperties and macroproperties of the RAC was discussed. The results showed that the modulus of the ITZs, the old mortar matrix and the new mortar matrix increased while the thickness of the ITZs decreased when the carbonation pressure or carbonation duration were increased. However, there was no further significant change after the carbonation pressure exceeded 1 bar, and the carbonation rate began to decrease significantly after 3 h of carbonation. The carbonation efficiency was superior when the moisture content was 1.81%. The effects of different carbonation parameters on the microproperties and macroproperties of the RAC were consistent. The compressive strength and chloride ion penetration resistance of the RAC had a linear correlation with the modulus of the ITZ between the aggregate and old mortar.

Microstructure and macro properties of sustainable alkali-activated fly ash mortar with various construction waste fines as binder replacement up to 100%

Abstract: Utilizing construction waste fines as eco-friendly binder for sustainable alkali-activated materials provides new approach to recycling construction waste. This work investigated the characterization of alkali-activated fly ash mortar (AAM) incorporating construction waste fines at varied types and replacement levels. The results showed that incorporating waste paste powder containing abundant hydrated products refined the pore size of AAM, but mixing waste mortar powder and waste concrete powder that contained massive inert quartz and calcite adversely affected the alkali-activated reaction and pore structure of AAM. The incorporation of construction waste fines was found to reduce the fluidity but increased the drying shrinkage of AAM. At identical replacement level of construction waste fines, the waste paste powder incorporated AMM has lower fluidity and greater drying shrinkage than the waste mortar powder or waste concrete powder incorporated AAM. Substituting waste paste powder for fly ash improved the mechanical strength of AAM, but the strength decreased as waste mortar powder or waste concrete powder was incorporated. Particularly, the AAM blended with 100% construction waste fines still owned good strength. Mixing construction waste powder reduced the chloride diffusion coefficient and chloride ingress depth of AAM, and the waste paste powder mixed AAM had better chloride resistance than the waste mortar powder or waste concrete powder mixed AAM. Therefore, the hydrated products in construction waste fines was revealed to benefit the micro-characteristics of alkali-activated materials, and optimizing the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.

A Step towards Sustainable Concrete with Substitution of Plastic Waste in Concrete: Overview on Mechanical, Durability and Microstructure Analysis

Abstract: Plastics have become an essential part of our daily lives, and global plastic production has increased dramatically in the past 50 years. This has significantly increased the amount of plastic garbage produced. Researchers have recently been interested in using trash and recyclable plastics in concrete as an ecologically acceptable building material. A large number of publications have been published that describe the behavior of concrete, containing waste and recovered plastic com ponents. However, information is scattered, and no one knows how plastic trash behaves as concrete materials. This research examines the use of plastic waste (PW) as aggregate or fiber in cement mortar and concrete manufacturing. The article reviewed the three most significant features of concrete: fresh properties, mechanical strength, and durability. PW and cement connections were also studied using microstructure analysis (scan electronic microscopy). The results showed that PW, as a fiber, enhanced mechanical performance, but PW, as a coarse aggregate, impaired concrete performance owing to poor bonding. The assessment also identified research needs in order to enhance the performance of PW-based concrete in the future.

A Multi-objective Optimisation Approach for Activity Excitation of Waste Glass Mortar

Abstract: Waste glass is promising to be recycled and reused in construction for sustainability. Silicon dioxide is the main component of glass, however, its pozzolanic activity is latent mainly due to its stable silica tetrahedron structure. To excite the activation of waste glass, chemical activation and mechanical grinding of waste glass powder (WGP) were investigated. As the supplementary, hydrothermal and combined (mechanical-chemical-hydrothermal) treatments were conducted on part of the WGP samples. The unconfined compression strength (UCS), expansion caused by alkali–silica reaction (ASR), and the microstructural morphology of WGP were investigated. The results showed the dosage threshold (around 2%) of the chemical activators (alkali and sodium sulfate) and the combined activation were optimal. Besides, a firefly algorithm (FA) based multi-objective optimisation model (MOFA) was applied to seek the Pareto fronts based on three objectives: UCS, ASR expansion, and Cost of mixture proportion. The objective functions of UCS and expansion were established through training the machine learning (ML) models where FA was used to tune the hyperparameters. The cost was calculated by a polynomial function. The ultimate values of root mean square error (RMSE) and correlation coefficient (R) showed the robustness of the ML models. Moreover, the Pareto fronts for mortars containing 300 μm and 75 μm WGPs were successfully obtained, which contributed to the practical application of waste glass in mortar production. In addition, the sensitivity analysis was conducted to rank the importance of input variables. The results showed that curing time, activator's content, and WGP particle size were three essential parameters.

Effect of alum sludge ash on the high-temperature resistance of mortar

Abstract: The effect of high temperature on the mechanical, durability, and microstructural properties of mortar containing alum sludge ash (ASA) was investigated in this paper. The ASA was derived from grinding and calcinating alum sludge, a typical by-product of the drinking water treatment processes. Four different mortar mixtures with ASA content at weight percentages of 0%, 10%, 20%, and 30% (as cement replacement) were exposed to high temperatures of 300 °C, 550 °C, and 800 °C, respectively. The experimental results showed that mortar samples containing up to 20% of cement replaced with ASA exhibited superior high-temperature resistance to the reference ones (without ASA), especially after exposure to 800 °C. The thermal analysis determined the portlandite consumption because of ASA pozzolanic reaction, and the x-ray diffraction pattern showed that the ASA reaction might contribute to the formation of aluminum-bearing phases with excellent refractoriness in the binder matrix. In addition, crack examination conducted by backscattered electron images evidenced that the ASA addition mitigated the binder paste degradation.

Effect of alum sludge ash on the high-temperature resistance of mortar

Abstract: The effect of high temperature on the mechanical, durability, and microstructural properties of mortar containing alum sludge ash (ASA) was investigated in this paper. The ASA was derived from grinding and calcinating alum sludge, a typical by-product of the drinking water treatment processes. Four different mortar mixtures with ASA content at weight percentages of 0%, 10%, 20%, and 30% (as cement replacement) were exposed to high temperatures of 300 °C, 550 °C, and 800 °C, respectively. The experimental results showed that mortar samples containing up to 20% of cement replaced with ASA exhibited superior high-temperature resistance to the reference ones (without ASA), especially after exposure to 800 °C. The thermal analysis determined the portlandite consumption because of ASA pozzolanic reaction, and the x-ray diffraction pattern showed that the ASA reaction might contribute to the formation of aluminum-bearing phases with excellent refractoriness in the binder matrix. In addition, crack examination conducted by backscattered electron images evidenced that the ASA addition mitigated the binder paste degradation.

Statistical Methods for Modeling the Compressive Strength of Geopolymer Mortar

Abstract: In recent years, geopolymer has been developed as an alternative to Portland cement (PC) because of the significant carbon dioxide emissions produced by the cement manufacturing industry. A wide range of source binder materials has been used to prepare geopolymers; however, fly ash (FA) is the most used binder material for creating geopolymer concrete due to its low cost, wide availability, and increased potential for geopolymer preparation. In this paper, 247 experimental datasets were obtained from the literature to develop multiscale models to predict fly-ash-based geopolymer mortar compressive strength (CS). In the modeling process, thirteen different input model parameters were considered to estimate the CS of fly-ash-based geopolymer mortar. The collected data contained various mix proportions and different curing ages (1 to 28 days), as well as different curing temperatures. The CS of all types of cementitious composites, including geopolymer mortars, is one of the most important properties; thus, developing a credible model for forecasting CS has become a priority. Therefore, in this study, three different models, namely, linear regression (LR), multinominal logistic regression (MLR), and nonlinear regression (NLR) were developed to predict the CS of geopolymer mortar. The proposed models were then evaluated using different statistical assessments, including the coefficient of determination (R2), root mean squared error (RMSE), scatter index (SI), objective function value (OBJ), and mean absolute error (MAE). It was found that the NLR model performed better than the LR and MLR models. For the NLR model, R2, RMSE, SI, and OBJ were 0.933, 4.294 MPa, 0.138, 4.209, respectively. The SI value of NLR was 44 and 41% lower than the LR and MLR models’ SI values, respectively. From the sensitivity analysis result, the most effective parameters for predicting CS of geopolymer mortar were the SiO2 percentage of the FA and the alkaline liquid-to-binder ratio of the mixture.

Thermal insulation and mechanical characteristics of cement mortar reinforced with mineral wool and rice straw fibers

Abstract: Building insulation is an essential requirement for buildings located in areas of varying temperature conditions. However, the conventional building insulation techniques accrue high cost and consume resources. This work aimed to evaluate the use of mineral wool and rice straw to improve Portland cement mortar's thermal insulating properties. Samples of 40x40x160 mm mortar were produced with cement and sand, but varying mineral wool and rice straw constituents from 0 to 50% in weight. Water absorption, flexural and compressive strengths , thermal conductivity were performed in samples with and without mineral wool and rice straw addition. The microstructure of mortars was analyzed using scanning electron microscopy (SEM). It was observed that reinforcing mortars with mineral wool and rice straw fibers yielded a significant drop in the mortar's thermal conductivity, improving their insulative abilities. Although the addition of fibers, in turn, deferred the mechanical performance in some mixes, however, it was not too significant or below workable standards. The performed tests prove the feasibility of adopting the selected fibers for insulating Portland cement mortars. • Mineral wool and rice straw as thermal insulation enhancer. • Thermal conductivity of mortar reduced with fiber additions. • Rice straw and mineral improved mechanical properties of mortars.

Mix design and performance of lightweight ultra high-performance concrete

Abstract: The inferior mechanical properties and durability of conventional lightweight concrete restrict its wider application. This study intended to design a novel lightweight ultra high-performance concrete (L-UHPC) using a mathematical approach, with a view to achieving low density and excellent performance. Two lightweight materials (i.e. micro-sized glass microsphere and expanded shale aggregates) were introduced in the mix design of L-UHPC. The statistical optimization via Central Composite Design was proved to be an effective method to produce the L-UHPC. The designed L-UHPC showed comparable or even superior functional and durability properties than normal-weight UHPC and high-performance cement mortar. The use of specified lightweight materials played prominent roles in ensuring the mechanical properties of L-UHPC. The high microhardness of paste matrix and the internal curing of lightweight aggregates contributed to the great durability of L-UHPC. The development of L-UHPC can provide a new solution for constructing high-performance lightweight structures and composites.

Clays and Clay Minerals in the Construction Industry

Abstract: Clay is a naturally occurring material that can be converted to different clay minerals through thermal treatments, and can be used for the development of different products. Clays and clay minerals have been used for different applications in different sectors. Detailed information regarding the applications of these materials in the construction industry are described. Clay has been used as a supplementary cementitious material in Portland cement (OPC) mortars and concretes. These minerals decrease raw materials and CO2 emissions during the production of Portland cement clinker and, at the same time, increase the compressive strength of concrete at a later age. Therefore, they are conducive to the sustainability of construction materials. A new type of cement, Limestone calcined clay cement (LC3), and a binding material geopolymer cement have also been developed using clay minerals. The properties of these binders have been discussed. Applications of clay products for making bricks have are also described in this article.