Shrinkage Of Mortar Research Articles

Effects of Internal Curing by Silica-Containing Polyacrylamide Hydrogel Particles on Autogenous Shrinkage and Mechanical Strength of Mortar

Effects of Internal Curing by Silica-Containing Polyacrylamide Hydrogel Particles on Autogenous Shrinkage and Mechanical Strength of Mortar

Investigation of the Flow, Compressive Strength, Shrinkage, and Tensile Properties of Mortar with Internal Curing Bottom Ash

Investigation of the Flow, Compressive Strength, Shrinkage, and Tensile Properties of Mortar with Internal Curing Bottom Ash

Shrinkage and Mechanical Properties of Fibre‐Reinforced Blast Furnace Slag‐Steel Slag‐Based Geopolymer

Geopolymer materials have several obvious advantages such as energy conservation, emission reduction, and waste reuse, so they can become substitutes for cement materials. In this study, geopolymer mortars made from blast furnace slag and steel slag reinforced by basalt fibre and polyvinyl alcohol (PVA) fibre were prepared to explore the effect on their strength and shrinkage properties. Scanning electron microscopy (SEM) was employed to characterize the reaction mechanism of the geopolymer mortars. The results show that both PVA fibre and basalt fibre can improve the mechanical properties of geopolymer mortars during the late curing period. The geopolymer reinforced by basalt fibre manifested a better toughness. A proper content of PVA fibres and basalt fibres can effectively reduce the drying and autogenous shrinkage of geopolymer mortars. The optimal content of basalt fibres and PVA fibres to reduce the drying shrinkage was 0.4%. The SEM results show that the fibres can effectively alleviate the stress concentration and prevent crack propagation.

Drying shrinkage behavior of hybrid alkali activated cement (HAAC) mortars

Shrinkage is a vital factor for hybrid alkali activated cement (HAAC) related to durability. In this work, the drying shrinkage behavior of HAAC mortars with various precursors, curing regimes and activator states was investigated. Portland cement mortar and alkali activated cement (AAC) mortar were used as control groups. Results showed that the drying shrinkage magnitude of HAAC mortar is lower than that of AAC mortar but higher than that of Portland cement mortar. Slag-based HAAC mortar shows the largest shrinkage value and the introduction of fly ash could temper shrinkage slightly. The steam curing and solid activation could mitigate the magnitude of drying shrinkage for HAAC mortar. The drying shrinkage is irrespective of the water loss in this study. MIP, SEM, and XRD analyses were undertaken to gain more insights into the mechanisms of drying shrinkage of HAAC. More crystalline phase and higher Ca/Si gel of HAAC paste tempers the drying shrinkage of HAAC mortar. The larger capillary pores size is likely to explain the lower shrinkage of fly ash-based HAAC mortar.

Effects of silica fume and Fly ash on properties of mortar reinforced with recycled-polypropylene

Adding polypropylene (PP) plastic into concrete or mortar partially instead of sand is an effective way to recycle plastic waste, but its low strength is still a problem to be solved. This work investigated the possibility of improving the mechanical properties and inhibiting the shrinkage of cement mortar with recycled PP plastic by incorporating silica fume (SF) and fly ash (FA) into the mortar. An experimental study was conducted to evaluate the effects of SF, FA, and the composite admixture of SF and FA on the fluidity, physical properties, mechanical properties, compressive strength, flexural strength, and microstructure of PP-filled cement mortar. The results showed that the addition of SF or FA reduced the porosity and water absorption of the PP-filled mortar. The combination of SF and FA reduced the porosity and water absorption, improved the compressive and flexural strength, and promoted the strength development of the PP-filled mortar in later stage. Compared with control group, the 28-d compressive strength and flexural strength of PP-filled mortar with 7% SF and 15% FA increased by 10.04% and 8.48%, and its 56-d autogenous shrinkage just increased by 1.62% and drying shrinkage decreased by 3.23%. Considering the strength and shrinkage characteristics, the optimal combination contents of SF and FA were 7% and 15%, respectively. Adding SF and FA into PP-filled mortar provides a new solution to solve the problems of low strength and large shrinkage of plastic mortar, which can not only promote the application of plastic waste in mortar, but also consume the industrial wastes, and protect the ecological environment.

Strength of the flexural joint of mortar joints and solid fired clay brick prisms

Masonry constructions built with mortar and solid fired clay bricks are subject to: high cement content, excessive water-cement ratio causing problems of mortar shrinkage during curing and differential movements between the brick and mortar caused by movements due to wind or seismic events. Earth movements generate some failures in simple masonry walls and confined masonry in solid brick joints, mainly with failure inclination angles varying from 45 degrees to 50 degrees. The objective of this research work was to estimate the flexural bond strength of the mortar joint and the solid fired clay brick and thus establish design parameters for non-structural masonry in the municipality of Ocanña, Colombia. From the fired clay brick manufacturers, 18 in total, simple random sampling was used to determine the sample size, 4 manufacturers were randomly selected. In addition, the characterization of the solid fired clay brick units was carried out with respect to their compressive strength, initial absorption rate and final absorption, as well as the mortar with respect to its compressive strength at 28 days, according to the Colombian standard for earthquake resistant constructions; for the determination of the flexural strength of the bonding mortar and solid brick units, a semiautomatic machine for flexural strength testing of masonry units, Pinzuar model PC-13, with a force measurement of 1000 N and an accuracy of 0.1 N, was designed. The flexural strength at the masonry joint was obtained for mortar type M with a value of 0.26 MPa, with a standard deviation of 0.01 MPa and a coefficient of variation of 4.72%. As for mortars type N and S, the average strength value was equal to 0.24 MPa for the two types of mortar, with standard deviation of 0.03 MPa and 0.01 MPa respectively, and coefficient of variation of 11.4% and 3.18% respectively. Given the importance of the variables, an interpretation of physical of the relationship between the properties was made: compressive strength of the solid fired clay brick and flexural strength at the masonry joint, since their average values were similar.

Mechanical strengths, drying shrinkage and pore structure of cement mortars with hydroxyethyl methyl cellulose

This paper aims at investigating the long-term mechanical strengths and drying shrinkage, as well as pore structure of cement mortars with hydroxyethyl methyl cellulose (HEMC). The results show that the 3-d flexural strength and compressive strength of cement mortars tend to decrease with the HEMC content increasing. At 28 d to 360 d, the strengths keep decreasing with the HEMC content increasing at 0–1%, and then increase from the minimum value with the HEMC content increasing at 1–3%, still being much lower than those of the control (0% HEMC). Throughout the curing age, both the tensile bond strength and the drying shrinkage value gradually increase with the HEMC content, to be nearly twice at 3% HEMC than those of the control. HEMC significantly delays the 3-d hydration of cement pastes, but has negligible retardation effect on the hydration after 28 d, to bring the similar late hydration degree of cement pastes with HEMC or not. With the HEMC content increasing in the range of 0–1%, incorporating HEMC brings the sharp increase of macro pores, large capillary pores and porosity, and decreases the interconnected pores to bring many more closed pores. Further increasing the HEMC content to 3%, macro pores and porosity decrease, large capillary pores slightly increase and interconnected pores have a negligible change. Obviously, the understanding on the performance development of cement mortars with HEMC is conducive to the better application of HEMC in dry-mix mortars to meet different requirements.

Influence of Microfibrillated Cellulose Additive on Strength, Elastic Modulus, Heat Release, and Shrinkage of Mortar and Concrete.

This work aimed to study the effect of a microfibrillated cellulose additive on strength, elastic modulus, heat release, and shrinkage of mortar and concrete. The dosage of the additive varies from 0.4 to 4.5% by weight of the cement. The change in strength with an increase in the dosage of the additive occurred in a wave-like manner. The uneven character of the change in the results also took place in the determination of heat release and shrinkage. In general, heat release and shrinkage decreased at increasing additive dosage. The additive showed the greatest decrease in the heat release of concrete at a content of 2%. The heat release of concrete practically differed little from the exotherm of the standard at an additive content of 1 and 1.5%. The addition of microfibrillated cellulose additive in small (0.5%) and large (1.5%) amounts reduced shrinkage compared to the reference, and at an intermediate content (1%), the shrinkage was higher than in the reference specimens. In this case, the water evaporation rate from concrete increased with an increase in the additive. With an increase in the additive dosage, the modulus of elasticity decreases. Thus, the microfibrillated cellulose additive provides concrete with lower values of the modulus of elasticity, heat release, and shrinkage, and the additive is recommended for use in concretes with increased crack resistance during the hardening period. The recommended additive content is 0.5% by weight of cement. At the specified dosage, it is possible to provide the class of concrete in terms of compressive strength C35/45.

Particle Size Effect of Oyster Shell on Mortar: Experimental Investigation and Modeling.

In order to solve the problem of lack of natural river sand, crushed waste oyster shells (WOS) were used to replace river sand. By replacing 20% river sand, WOS mortar with different particle sizes of WOS were made for the experiment. Through experimental observation, the initial slump and slump flow loss rate were studied. The effects of different particle sizes and curing times on the compressive strength, flexural strength, static elastic modulus, and dry shrinkage of WOS mortar were analyzed. The relationship formulas between the compressive strength, flexural strength, particle size, and curing age were proposed. The results showed that the setting time and slump flow decreased with a decrease in the particle size of WOS. It was also found that the mortar with fine crushed WOS had high compressive strength, flexural strength, and static elastic modulus at both early and long-term curing age. A formula was proposed to describe the development of the compressive strength with the particle size of WOS and curing time, and the relations among these mechanical properties were discussed. Furthermore, drying shrinkage increased when WOS was used and could not satisfy the standard requirement of 0.075%. In contrast, the addition of fine WOS and double-dose sulfonated naphthalene-formaldehyde superplasticizer (SNF SP) reduced the shrinkage rate of the mortar by 8.35% and provided better workability and mechanical properties for mortar.

Substitution of limestone filler by waste brick powder in self-compacting mortars: Properties and durability

The feasibility of using waste brick powder (WBP) in the manufacture of self-compacting mortar has been investigated in this study. The limestone filler was partially or totally (0%, 50% and 100%) substituted with WBP. The rheological properties, compressive and flexural strengths, drying shrinkage and durability properties (including carbonation resistance, chloride ion diffusion and sulphate resistance) of self-compacting mortars were evaluated. The WBP-mortars presented a higher yield stress and plastic viscosity than that of WBP-free mortar: the additional water has to be added in order to achieve the equivalent workability. The compressive strength of WBP-mortars slightly decreased after 7 days (the compressive strength of series mortars M − BP decreased 5.6% and 9.3% for 50% and 100% WBP based mortars comparing with the reference mortar, respectively; while the compressive strength of series with similar workability mortar M-BP100WA which was based on 100% WBP decreased 16.7% and it could achieve 26.8 MPa), but the decreasing trend seemed to be compensated by the pozzolanic activity of WBP and remained equivalent after 28 days (the compressive strength of series mortar M-BP100WA decreased 5.3% and it could achieve 35.6 MPa). The substitution of limestone filler by WBP didn't seem to impair the durability behavior of mortars (except for the resistance to carbonation). Therefore, it is possible to manufacture self-compacting mortar by partially or totally substituting limestone filler by WBP.

Strength behavior and autogenous shrinkage of alkali-activated mortar made from low-calcium fly ash and calcium carbide residue mixture

In this study, the effects of sodium hydroxide (NaOH) concentrations, ratios of low-calcium fly ash (FA) to calcium carbide residue (CR), and adding 5% of Portland cement on compressive strength and autogenous shrinkage of alkali-activated mortar made from FA-CR mixtures were investigated and verified by examining the microstructure and morphology of alkali-activated paste. Both FA and CR were improved by grinding a finer powder. The alkali activators were a NaOH solution and a liquid sodium silicate at a constant ratio of 2:1. The results indicated that the utilization of CR partially substituted in FA and activated with a higher NaOH concentration significantly improved the compressive strength of alkali-activated mortars. The autogenous shrinkage of alkali-activated mortars increased with the increased NaOH concentration and decreased significantly when the CR partially replaced in FA. An alkali-activated mortar made from an FA-CR mixture (without cement) achieved compressive strengths up to 60.2 MPa and had an autogenous shrinkage of less than 100 × 10−6 mm/mm. Moreover, the XRD patterns of alkali-activated pastes showed that the reaction products of C–S–H, C–A–S–H, and N–A–S–H were related to the dense structure and the Si, Al, Ca, and Na detected in SEM/EDS results.

Influence of a polyurethane‐modified polycarboxylate on properties of cement mortar

AbstractIn this article, a new kind of polycarboxylate (M‐PCE) was synthesized at room temperature in the complex initiation system of hydrogen peroxide (H2O2), ascorbic acid (Vc) and ammonium persulfate (APS), by using polyoxyethylene allyl methyl ether (TPEG), acrylic acid (AA), polyethylene glycol (PEG) as raw materials and thioglycolic acid (TGA) as chain transfer agent. Effect of different composite initiation systems and raw material ratios were fully explored. Along with three other polycarboxylates (O‐PCE, C‐PCE‐1, and C‐PCE‐2), their properties on water reduction rate, strength, drying shrinkage and autogenous shrinkage of cement mortar were investigated. The results showed that the average performance of the prepared M‐PCE was the best when the molar ratio of AA to TPEG was 2:1 in the same situation. When the water cement ratio was 0.3 and the dosage of M‐PCE was 1%, the strength increased by 24.5%(with 10% slag), the lowest drying shrinkage and autogenous shrinkage were reduced by 21.9%(with 10% fly ash) and 60.1%(with 10% metakaolin), respectively.

Improving the cracking resistance of mortar by reduced graphene oxide

The shrinkage cracking adversely impacts the long-life durability of cement composites. However, how to restrict the formation and evolution of cracking is still a challenge. Herein, we propose a new strategy to control the shrinkage strain and associated cracking of cement mortar by introducing reduced graphene oxide (rGO). The early-age shrinkage and cracking resistance experimentation of mortar are firstly investigated. Moreover, the shrinkage mechanism is carried out and the distribution of rGO in mortar matrix is analyzed by scanning electron microscopy and X-ray micro-computed tomography. The results show rGO aggravates the imbalance relationship of evaporation-bleeding water on the surface of mortar, which increases the plastic shrinkage value. The water retention effect of rGO contributes to the decrease of autogenous and drying shrinkage. The well-dispersed rGO reduces the number, total length and width of plastic shrinkage cracking. In conclusion, the incorporation of rGO enhances the cracking resistance of mortar and exhibits a promising potential for the long-term sustainable development of cement composites.

Effect of Recycled Aggregate Carrying Sulfate Corrosion Media on Drying and Autogenous Shrinkage of Mortar

In this study, the effects of recycled sand (RS) carrying sulfate corrosion media on mortar drying and autogenous shrinkages were investigated. Four variables were considered, the replacement percentage of RS, water to cement (W/C) ratio, secondary cementitious material, and the corrosion concentration of RS. The test results indicated that the replacement percentage of RS was positively related to the drying and autogenous shrinkages of the mortar. The drying shrinkage of the mortar increased with an increase in the W/C ratio, while the autogenous shrinkage showed an opposite trend. The addition of fly ash (FA) had a significant inhibitory effect on the drying and autogenous shrinkages of the mortar. The drying shrinkage of the mortar was reduced, while the autogenous shrinkage was increased by adding granulated blast-furnace slag (GBFS). The addition of both FA and GBFS caused an increase in the autogenous shrinkage. As the corrosion concentration of RS increased, the drying and autogenous shrinkage values decreased slightly. The scanning electron microscopy and X-ray diffraction analysis results showed that the corrosion products formed by the reaction of sulfate ions carried by RS and cement hydration products filled the internal pores of the mortar and slowed down the shrinkage of the mortar.

Effect of alkali-resistant glass fiber and silica fume on mechanical and shrinkage properties of cement-based mortars

Fiber-reinforced concrete is widely applied owing to its significant mechanical properties and great resistance to cracking. However, the alkaline environment of pore solutions adversely affects the fibers, which reduces the concrete strength and durability. Considering this, alkali – resistant (AR) glass fiber (GF) materials, including both GF and glass fiber powders (GFP), were used to improve the condition. Furthermore, the co-efficient of AR-GF and silica fume (SF) was studied. For each material, three replacement levels were designed, and 10 groups of specimens were cast in this experiment. The compressive strength, flexural strength, autogenous shrinkage, and drying shrinkage of mortars were measured, at the same time, microstructure of some presentive samples was observed through scanning electron microscopy (SEM) tests. The experimental results showed that GF has a great effectiveness on enhancing the mechanical properties of mortars, especially to flexural strength, for which 57% improvement was observed under 28d curing when 7.5% GF was added. Meanwhile, AR-GFP showed the extrordinary effect on mitigating the mortars’ shrinkage. 40% autogenous shrinkage and 50% drying shrinkage were eliminated when 5% GFP was incorporated in mortars. However, the effectiveness was reduced with continuous increase of GFP. Unsurprisingly, the mechanical properties of mortars with GF was further improved when SF was added into mortar, in which additional 50% enhancement of flexural strength and 10% enhancement of compressive strength were achieved. However, SF refined the pore size of mortars which resulted in the increase of autogenous shrinkage and drying shrinkage. In a short, The use of AR fiber materials and SF improved the mortars’ mechanical properties and durability, which has a high practical value.

The effect of polypropylene fiber with different length and dosage on the performance of alkali-activated slag mortar

Alkali-activated slag (AAS) cement is a cementitious material with high strength, high durability and environmental protection. AAS is considered as a potential substitute for Ordinary Portland Cement, although its large-scale application is limited by its large drying shrinkage. In this study, we demonstrate that the addition of polypropylene fiber (PPF) can reduce the drying shrinkage of AAS mortar. The influences of PPF length and dosage on the fluidity, mechanical properties, microstructure and impact resistance of AAS mortar are investigated. Three lengths (3 mm, 9 mm and 15 mm), and four dosages (volume fractions of 0.05%, 0.1%, 0.15% and 0.2%) of PPF are used in the AAS mixtures. Test results show that the addition of PPF can reduce the drying shrinkage of AAS mortar, as adding 0.2% of 15 mm PPF can reduce the drying shrinkage by 37.1%. The flexural strength of AAS mortar increases with PPF length and dosage, while introducing long PPF (9 mm and 15 mm) can slightly improve the compressive strength of AAS mortar. Mercury intrusion porosimetry (MIP) and Scanning electron microscope (SEM) results indicate that PPF with 9 mm and 15 mm can reduce the average pore size and improve the microstructure of AAS mortar. At the same time, effective bonding between the matrix and PPF is observed, which is consistent with the enhancement of mechanical properties. Furthermore, PPF addition significantly improves the ultimate toughness of the AAS mortar, which is manifested in the enhancement of impact resistance.

Effect of Amorphous Metallic Fibers on Strength and Drying Shrinkage of Mortars with Steel Slag Aggregate.

Recently, with increasingly stringent environmental regulations and the depletion of natural aggregate resources, high-quality aggregates have become scarce. Therefore, significant efforts have been devoted by the construction industry to improve the quality of concrete and achieve sustainable development by utilizing industrial by-products and developing alternative aggregates. In this study, we use amorphous metallic fibers (AMFs) to enhance the performance of mortar with steel slag aggregate. Testing revealed that the 28-day compressive strength of the sample with steel slag aggregate and AMFs was in the range of 48.7–50.8 MPa, which was equivalent to or higher than that of the control sample (48.7 MPa). The AMFs had a remarkable effect on improving the tensile strength of the mortar regardless of the use of natural aggregates. With AMFs, the drying shrinkage reduction rate of the sample with 100% steel slag aggregate was relatively higher than that of the sample with 50% natural fine aggregate. Furthermore, the difference in the drying shrinkage with respect to the amount of AMFs was insignificant. The findings can contribute to sustainable development in the construction industry.

Predicting shrinkage of alkali-activated blast furnace-fly ash mortars using artificial neural network (ANN)

Drying shrinkage of alkali-activated binders are recognized as one of the most important properties towards quality assurance of the binders. In this study, results of experimental studies and predictive models developed to determine the drying shrinkage of alkali - activated blast furnace-fly ash mortars are presented and discussed. Different parameters were altered in the experimental study such as the content of GGBFS, FA, activator modulus (Ms), and curing temperature. Their effects on the drying shrinkage of the mortars were then evaluated. Artificial neural network (ANN) and Multiple Linear Regression (MLR) models were built to predict the drying shrinkage at 28 days using the above-mentioned parameters as inputs. The experimental results and ANN model predictions showed strong correlations. The prediction of 28-days drying shrinkage for the alkali-activated GGBFS-FA was more accurate using ANN than MLR.

Effects of triethanolamine on autogenous shrinkage and drying shrinkage of cement mortar

Impacts of triethanolamine (TEA) on autogenous shrinkage, drying shrinkage and strength development of cement mortars were investigated. Hydration kinetics, pore structure and microstructure of hardened cement pastes (hcps) incorporated with TEA were systematically analyzed to reveal the working mechanism of TEA. Results show that TEA at dosages of 0.05%, 0.10% and 0.50% by weight of cement increases the autogenous shrinkage of cement mortars at 7d, which is mainly resulted from the promoting effect of TEA on the secondary hydration of aluminate phases (C3A and C4AF) and inhibiting effect on the hydration of the silicate phase (C3S) especially at 0.50% dosage. The morphology change of CH in the presence of TEA may also accelerate the development of autogenous shrinkage. In addition, TEA has no obvious effect on the drying shrinkage of cement mortars due to the similar moisture diffusion trends of cement mortars with and without TEA from 7d to 56d. Moreover, 0.05% and 0.10% TEA enhance the early strength of cement mortars while 0.50% TEA leads to an opposite effect. However, 0.05%, 0.10% and 0.50% TEA reduce the late strength at 28d and 56d. Pore structures are not responsible for the strength reduction, as indicated from the MIP and DVS results. Therefore, it is believed that strength reduction may be resulted from the incorporation of CH microcrystals into C-S-H structures.

Influences of shrinkage reducing admixture on the mechanical properties, drying shrinkage, water absorption and porosity of Portland cement mortar

Drying shrinkage is the main cause of early age cracking of concrete and mortar. A wide range of research has been conducted to reduce the drying shrinkage, including using fibres or chemical admixtures. This paper investigated the effect of shrinkage reducing admixture on the flexural strength, compressive strength, drying shrinkage, water absorption and porosity of mortar. The mix compositions were ordinary Portland cement (OPC) : sand : liquid = 1: 1: 0.38 in which liquid consisted of water and shrinkage reducing admixture (SRA). SRA was used at the proportions of 2%, 4%, and 7% by weight of cement. The test results show that SRA reduces the flexural and compressive strengths of mortar. The reduction in flexural strength and compressive strength at 28 days is 14% and 25%, respectively at 7% SRA dosage. In addition, SRA significantly reduces the drying shrinkage and water absorption of mortar. At 7% SRA dosage, the drying shrinkage at 53 days is reduced by 60% while the water absorption rate at 24 hours is reduced by 54%. However, SRA has a minor effect on the pore size distribution, effective porosity, and cumulative intrusion volume of mortar.