Behavior Of Mortar Research Articles

Effect of organic corrosion inhibitors on the behaviour of repair mortars and reinforcement corrosion

Repairing concrete structures affected by reinforcement corrosion is vital to ensure their durability and safety. Organic corrosion inhibitors (OCIs) are widely used in the construction industry to prevent steel corrosion due to their effectiveness, sustainability, and health and safety benefits. However, the effects of these OCIs on different types of repair mortars have not been extensively studied. This study evaluated the fresh and hardened properties, as well as the corrosion resistance, of four types of repair mortars (polymer-modified, general cementitious, fine-grained, and alkali-activated) incorporated with two types of OCIs (amino alcohols and sodium gluconate-based) at dosages of 0.5 %, 1 %, and 2 %. Additionally, the corrosion kinetics of mortars under the influence of OCIs were analysed using the impressed current technique. The results indicated that OCIs generally enhanced workability and increased void content across all repair mortars. The amino alcohol inhibitor increased the drying shrinkage of general cementitious and fine-grained mortars by up to 33 % and 39 %, respectively, and reduced compressive strengths by 47 % and 26 %. However, it did not significantly affect water absorption. In contrast, the sodium gluconate inhibitor increased water absorption in all repair mortars but notably decreased drying shrinkage by up to 47 % in polymer-modified mortar and 66 % in alkali-activated mortar. Despite the variations in the properties of repair mortars, OCIs effectively resisted corrosion and delayed crack formation time by up to 400 %. The resistance to corrosion improved with increasing amounts of the inhibitor. The results of this study were used to develop a technical guide for the construction industry, facilitating the selection of appropriate mortar compositions to effectively repair corroded concrete structures and reduce the risk of further corrosion.

Three-dimensional mesoscopic investigation on the dynamic compressive behavior of coral sand concrete with reinforced granite coarse aggregate (GCA)

In the construction of island and reef engineering, coral concrete shows a good application prospect due to its abundant raw materials. However, the porous and fragile mechanical characteristics of coral reefs limit their use as coarse aggregate in the preparation of coral concrete materials. This study utilized hard and dense granite as the coarse aggregate and regarded coral sand concrete as a two-phase composite material consisting of spherical granite coarse aggregate (GCA) and coral mortar. It investigated the enhancement effect of granite on coral concrete from a microscopic perspective. Five 3D mesoscopic models with different GCA contents and randomly distributed aggregates were established to reveal the variation patterns and failure mechanisms of coral sand concrete under impact loading with GCA. The findings demonstrate that the K&C model can effectively simulate the dynamic compression behavior of coral mortar and granite materials. Under the action of a half-sine incident wave, the dynamic compressive strength of the samples increases with the increase in GCA, demonstrating that the addition of GCA can effectively enhance the impact resistance of coral sand concrete. As the content of GCA increases, the sensitivity of the samples to the loading wave amplitude also increases accordingly.

Influence of polyethylene terephthalate (PET) flakes coating on the microstructure and mechanical properties of alkali activated composites

The objective of this research is the improvement of the mechanical strengths of the alkali activated slag composites with polyethylene terephthalate (PET) flakes content. The main drawback when large PET flakes (2–9 mm) are used in these composites is reduced adhesion between plastic surface and binding matrix. Therefore, the PET flakes were coated with two types of adhesives – based on polyvinyl acetate or sodium silicate solution, and then covered with fly ash, waste glass or slag powders. The microstructure (assessed by scanning electron microscopy) of interfacial transition zone between the PET flakes coated with waste glass and slag powders is denser than for uncoated PET flakes; this explains the improvement of the compressive strength of these mortars especially after longer curing times (28 days). The flexural strengths of the mortars with PET flakes are higher than for reference mortar (with sand aggregate) and the apparent density of the alkali activated composites with PET flakes are in general smaller than for the reference mortar. Thus, the coating of PET flakes improves the mechanical behaviour of mortars, preserving also a low apparent density. These results can lead to a wider recycling of PET waste, slag and waste glass powder, promoting circular economy and reducing the CO2 footprint without compromising the critical mechanical strength of mortars.

Investigating the interfacial vertical shear behavior of BFPMPC mortar and cement concrete with pothole repair

Magnesium phosphate cement (MPC) has both traditional cement properties and ceramic properties with fast setting and hardening characteristics. To rapidly reopen traffic and extend its service life, MPC has been widely used in the rapid repair of highway and airport cement concrete pavement. This study utilizes basalt fiber-reinforced polymer-modified magnesium phosphate cement (BFPMPC) developed in previous research to rapid repair the typical potholes on cement concrete pavement, aims to reveal the interface properties between BFPMPC mortar and cement concrete and further investigate the underlying mechanisms for such properties. Firstly, the optimal mixture ratio was determined by orthogonal test design. Then, the shear strength of the repair interface was measured by composite BFPMPC mortar and cement concrete specimens. The mechanical characteristics of the repair interface and the microscopic mechanism were characterized by nano-indentation technology and SEM/EDS. Finally, the interface constitutive model was established by DIGIMAT and finite element model was developed to simulate the interface failure. Results showed that the no new hydration products were produced by the addition of polymer in BFPMPC. BFPMPC matrix became denser with the increase of age, resulting in the better bonding between fiber and paste. The interface vertical shear strength at 6 h and 3 d were 3.1 MPa and 3.9 MPa, respectively. SEM/EDS results showed that polymer has a certain self-healing ability to decrease the crack width with increase of curing age, and a variety of inclusions in the repair interface were observed. The elastic modulus of each inclusion phase can be effectively analyzed by nanoindentation. The simulation results showed that the pressure on upper surface of BFPMPC mortar transfers to the bottom through the repair interface. As the tensile stress on the bottom over the maximum interface tensile stress, the cracks were extend from the bottom to upper, then the structure was failed. Interface vertical shear strength of numerical simulation was, respectively, 3.149 MPa and 3.957 MPa. It is close to the plain shear strength experimental value, validating the proposed interface constitutive relationship.

Effect of particle size and replacement ratio on mechanical performance of cementitious mortar containing ground recycled acrylonitrile butadiene styrene (GRABS) waste plastics

While waste plastics have been used as a natural sand aggregate replacement in cementitious mortar as a sustainable option to mitigate global accumulation of plastic waste in landfills, fundamental mechanical properties like compressive, tensile, and shear must be known to advance design and practical application of these cement-concrete composites as suitable building construction materials. Experimental testing is conducted to reveal to what extent the cementitious composite properties are altered, thereby influencing their overall mechanical performance, when both ungraded and graded ground recycled acrylonitrile butadiene styrene (GRABS) plastic are employed as substitutes for natural aggregates. The novelty of this research lies in its pioneering investigation to quantify the effects of varying particle sizes and volume fractions of waste plastics acquired through mechanical recycling and their influences on the mechanical properties of mortars containing plastics as a composite material. The results from fresh and hardened material properties are compared to conventional mortar properties to examine the impact of various GRABS particle sizes and volume fractions on the overall material strength. While replacing sand with waste plastic generally reduced mechanical properties, the resulting mixes still met the minimum compressive strength (4060 psi [28 MPa]) as per ASTM C150 standards for Portland cement. Notably, graded plastic particles with sizes less than 0.024 in [0.6 mm] demonstrated an overall improvement in mechanical properties compared to ungraded particles. Failure mechanisms responsible for compressive, tensile, and shear damage development are discussed by analyzing the fracture surfaces, which provide insight into the intricate relationship between waste plastic size and distribution on the mechanical behavior of mortar. The findings indicate that GRABS waste plastics, when combined with sand at appropriate particle sizes and volume fractions, have the potential to create tailored mixes to meet minimum mix design standards for construction applications.

Influence of enforced carbonation on alkali-silica reaction: Performance and multi-scale mechanisms

Alkali-silica reaction (ASR) has emerged as one of the major concrete deterioration issues. Despite the extensive effort investments in ASR mitigation, the interaction between ASR and carbonation remains unclear. To investigate the role and mechanisms of early-age enforced carbonation in ASR, enforced carbonation conditions at 50 °C and 95 % RH with different CO2 concentrations up to 20 % were employed at two stages. The ASR mitigation efficacy was evaluated by monitoring the volume expansion and cracking behavior of mortars containing reactive aggregates. A comprehensive understanding was obtained by analyzing the evolutions of ASR gel's composition, molecular structure, and hygroscopicity. The results indicate that ASR can be effectively suppressed under carbonation with a 97.9 % decrease in ASR-induced volume expansion and fully suppressed cracking when the mortars were cured at 20 % CO2 for 30 days. The decreases in the Q3 polymerization sites and [K + Na]/Si ratios of the ASR products, as well as the 30.3 % reduction in water uptake capacity of ASR gels under carbonation, uncovered the underlying mechanisms for the mitigated ASR at multiple length scales.

Microstructural behavior of mortars containing thermo-activated crushed demolition residue (TCDR)

The construction industry has been constantly expanding and is, consequently responsible for a high consumption volume of natural raw materials and for generating large amounts of waste. In detriment of this scenario, this research proposes the reuse of Construction and Demolition Waste (CDW), especially that from plaster for making mortars. The residue was thermo-activated at 650 °C for a period of 2h, a heating rate of 10 °C/min, it was crushed in a jaw crusher and passed through an ABNT N° 16 sieve. The mortars were prepared with a (cement:sand) ratio of 1:6 by mass, the sand was partially replaced by the residue in proportions of 0, 10, 20 and 30%, using Ordinary Portland Cement (OPC). Tests were carried out on consistency index, mass density, incorporated air content, isothermal calorimetry, water retention, mass density in the hardened state, flexural strength, compressive strength, water absorption and void index, in addition to testing techniques characterization, such as laser granulometry, pozzolanic activity using the Modified Chapelle method and Lúxan method, X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) as well as Mercury Intrusion Porosimetry (MIP). It was possible to observe that the residue has amorphous phases, through XRD and heterogeneous nucleation of smaller particles, proven by the calorimetry test, contributing to the increase in mechanical strength. The results indicate that the mixture with 30% replacement achieved a greater increase in mechanical strength, lower absorption rates and consequently, a reduction in the distribution of pore sizes.

Effect of Deoxyribonucleic Acid on the Chloride Diffusion Behavior of Cement Mortar

Effect of Deoxyribonucleic Acid on the Chloride Diffusion Behavior of Cement Mortar

STUDY OF THE PROPERTIES OF MORTAR INCORPORATED FROM MELTED PLASTIC BAGS

The aim of this research is to study the physical-mechanical behaviour and durability of mortars containing melted plastic bags. To this end, 4cmx4cmx16cm test specimens of mortar containing cement or not and melted plastic bags at a mass ratio ranging from 10 to 25% of the mixture were produced. Compressive strength, flexural strength and acid durability were measured. The results show that the quantity of plastics in the mortars is inversely proportional to water absorption. Similarly, cementless mortars containing 25% plastic bags (MWC25) and cement mortars containing 25% plastic bags (CM25) gave maximum compressive strengths of 9.45MPa and 10.45MPa respectively. The durability test in a 5% sulphuric acid solution showed that CM25 and MWC20 lost 50% of their mass after 28 days.

Mesoscale modeling of new-to-old concrete interface under combined shear and compressive loads

A mesoscale model of new-to-old concrete interface under combined shear and compressive loads is established, and a parameter study is conducted to evaluate the influence of interface roughness, bond strength, and fracture energy. The mesoscale model is numerically generated using a random aggregate technique, in which the number of aggregates is calculated using the Fuller grading curve and Walraven formula and the aggregates are randomly placed using the Monte Carlo simulation. The concrete damaged plasticity model is employed to simulate the mechanical behaviors of new and old mortars, as well as the interfacial transition zone between the mortar and aggregate. The linear elastic model is utilized to simulate the behavior of aggregates, while the cohesive-friction model is employed to represent the behavior of new-to-old concrete interface. The effect of interface roughness, bond strength, and fracture energy on the interface shear strength and post-peak shear strength using the double-shear test specimens is investigated. The results indicate that increasing the roughness of old concrete surface leads to significant increases in both the interface shear strength and post-peak shear strength, but the larger interface roughness is not necessarily better. As the interface bond strength increases, the interface shear strength remains the same, whereas the post-peak shear strength shows a large increase with the lower interface roughness. Moreover, the interface fracture energy imparts the minimal influence on the interface shear strength and post-peak shear strength, but the higher interface fracture energy can improve the overall constitutive behavior of new-to-old concrete interface if the roughness of old concrete surface is low. The numerical mesoscale model presented can provide the theoretical guidance and technical support for effective design and construction of new-to-old concrete interface and structures.

Variations in the physical and mechanical behavior of basalt fiber reinforced NHL mortars exposed to different curing conditions

This paper investigates experimentally the short-term behavior of natural hydraulic lime (NHL) mortars reinforced with ballast fiber for use as structural repair mortars in historic and contemporary buildings. The physical and mechanical properties of mortar mixes reinforced with 0.143–0.215 mm equivalent thick and 12 mm long fibers in volumetric percentages of 1 %, as well as of unreinforced mortars, produced with different compaction methods and cured under different environmental conditions, have been evaluated. A cost-effectiveness analysis has also been carried out to determine the economic impact of these factors in their practical application. It is found that basalt fiber reinforcement provides lower water absorption coefficients and significantly improves the shore hardness, compressive strength, and post-critical flexural behavior of NHL mortars at early ages. Furthermore, it is observed that the compaction procedure can improve the packing density of the mortars providing higher densities, lower water absorption coefficients and higher mechanical strength values. Finally, it is verified that the curing parameters affect unevenly the basalt fiber reinforced NHL mortars and unreinforced NHL mortars, with greater deterioration being observed in the former when sufficient moisture is not ensured. Decreases in hardness, flexural and compressive strength, as well as increases in the water absorption coefficient are important. Consequently, the economic profitability of basalt fiber reinforcement depends on ensuring optimal moisture conditions during curing, especially when the mixes have already lost excess water after the first 2–3 days. The study provides quantitative and qualitative data to determine the appropriate curing parameters for basalt fiber reinforced NHL mortars that are viable in practice for their industrial performance.

Effects of Temperature and Clay on Hydration Behavior of Mortar: A Study Through Ultrasound Technique

Effects of Temperature and Clay on Hydration Behavior of Mortar: A Study Through Ultrasound Technique

Effect of Different Types of Paint on the Hygrothermal Behavior of Facade-Rendering Mortars in Brazil

Effect of Different Types of Paint on the Hygrothermal Behavior of Facade-Rendering Mortars in Brazil

Towards improved flexural behavior of plastic-based mortars: An experimental and modeling study on waste material incorporation

A considerable fraction of solid waste, which is harmful, chemically reactive, and infectious, is generated globally. The frequent deposition of these wastes in landfills has significant environmental and health consequences. This study aims to develop an environmentally conscious approach by incorporating finely ground waste materials, namely marble powder (MP), glass powder (GP), and silica fume (SF), into plastic waste (PW) based mortar to assess their efficacy in improving flexural strength (FS). Plastic waste mortar samples were cast using shredded PW, replacing sand in amounts ranging from 5 % to 25 %. The FS of these samples was measured after 28 days and used as a reference. MP, GP, and SF were individually incorporated into PW-based mortar formulations in varying quantities of 5–25 %, with increments of 5 %, by replacing cement. In PW-based mortar formulations, waste materials were also utilized in various combinations, including GP+SF, MP+SF, MP+GP, and MP+GP+SF. In addition, prediction models, including decision tree (DT) and artificial neural network (ANN), were constructed utilizing experimental data for the FS of PW-based mortar. The substitution of PW with sand reduces the FS of mortar samples. The research findings emphasize that optimal replacement levels for MP, GP, and SF in PW-based mortar mixtures, based on their ability to enhance FS, were 15 %, 10 %, and 15 % by cement mass, respectively. However, the cumulative incorporation of MP, GP, and SF in PW-based mortar suggests cement should not be replaced beyond 15 %, as it reduces the FS. Both prediction models exhibited a high degree of correlation with the coefficient of determination (R2) value of 0.925 for ANN and 0.959 for the DT model. The findings showed that MP, GP, and SF may be used in PW-based mortar to improve the FS while producing eco-friendly building material.

Long-term behavior of mortars experiencing delayed ettringite formation

Ettringite formation is an expansive reaction that causes cracking in the hydrated cementitious materials. This research has investigated the mechanisms of ettringite formation by examining the chemical and physical structure of the reactants and products involved in the process of late age (over 15 years) ettringite formation, and subsequent expansion and cracking. For this, seven different types of commercially available cement with their unique composition, and an elevated heat curing temperature of up to 100 °C were applied. The physical expansion of mortar bars due to delayed ettringite formation was monitored by the length change comparator. Environmental scanning electron microscopy (ESEM) was used to qualify and quantify changes in the microstructure and chemical composition of the cementitious matrix. Results revealed that the high-temperature heat curing accelerated the onset of expansion but limited the over-magnitude of the expansion. Results also revealed that the expansion may take years to initiate, likely due to a critical pore size threshold necessary to induce stresses. If expansion is delayed, the expansion magnitude is greater than those that expanded immediately.

Influence of geometric shape, pore structure and surface modification of recycled fine aggregate on the rheology behaviour and strength development of mortar

The complex physical properties of recycled fine aggregate affect the rheological and mechanical properties of mortar, thereby limiting its application in cement-based materials. This paper evaluated the geometric shape and pore structure of natural fine aggregate (NFA), recycled fine aggregate (RFA), and recycled fine aggregate modified by water glass (MRFA), and studied its water absorption and bulk density. The influence of complex physical properties of RFA before and after modification on the rheological behavior, strength development, and microscopic properties of mortar was analyzed. The rheological tests were carried out on the fresh mortar with 7 mixes, and the compressive strength and flexural strength of hardened mortar after curing for 3, 7 and 28 days were tested. The results shown that the modification of water glass has improved the water absorption and geometric shape of RFA to some extent, resulting in a small increase in the apparent viscosity and yield stress of recycled mortar compared to NFA mortar. When the replacement level of RFA was less than 30 %, the compressive strength of recycled mortar was 13 % higher than that of NFA mortar. As the replacement level increased to 40 %, the incorporation of water glass also helped to improve the mortar strength. The irregular geometric shape and high water absorption of RFA were conducive to achieving dense mechanical bonding and reducing the Ca/Si ratio in the interface transition zone.

Combined application of CDWs as precursors and aggregates in geopolymer composites: A comprehensive rheological analysis

The study of rheological characterization of construction and demolition waste (CDW)-based geopolymeric materials has gained interest due to digital innovation in construction and the increased focus on sustainable materials. Understanding the rheological behavior of these materials is essential due to their rapid geopolymeric reaction kinetics and viscosity behavior. This study investigated the impact of various CDW-based fine recycled aggregates, including crushed concrete aggregates (CRC), crushed ceramic-tile aggregates (CTA), and crushed brick aggregates (CBA), on the rheological behavior of geopolymer mortars (GPMs). Natural sand (NSA) was utilized as a reference for comparison purposes. In addition to CDW-aggregates, the GPMs were also made from optimized CDW-based precursors of brick waste powder (BP), ceramic-tile waste powder (TP), or concrete waste powder (CP). As a result, twelve different GPMs were considered, each containing 100 % individual CRC, CTA, and CBA fine aggregates, blended with BP, TP, and CP precursors. The study evaluated the relationship between the design variable of SiO2/Al2O3 molar ratio as well as the packing densities (PD) of GPM systems and their rheological characteristics, such as flow, apparent and plastic viscosity, yield and shear stresses, thixotropy and shear strains employing the compressible packing method. The results indicate that all GPMs possess shear-thinning or pseudoplastic characteristics. Enhanced SiO2/Al2O3 molar ratio generally resulted in increased rheological parameters. However, using TP as a precursor and CBA as fine aggregates in GPM matrices led to significant enhancement in rheological parameters due to the higher specific surface area of TP and the greater irregularity, convexity, and absorption capacity of CBA particles. Notably, although the enhanced non-colloidal frictional interactions and colloidal flocculation of CRC, CTA, and CBA resulted in reduced flow tendency of GPMs, they have been found to improve the thixotropy during the initial geopolymeric gelation stage.

Evaluating the sensitivity of direct shear testing of soils for rheological characterization of masonry mortars

The present work evaluated the applicability of the direct shear test of soils (ASTM D 3080) as an alternative for the rheological characterization of masonry mortars. The sensitivity analysis of the method for mortars was carried out by varying the particle size distribution of the sand and the water/dry material ratio, generating twelve different mixtures. In addition to a basic characterization, the shear test results were compared with those of the squeeze-flow test (ABNT NBR15839). For squeeze-flow, 24 tests were carried out with two speeds (0.1 and 3 mm/s), and for direct shear, 48 tests were carried out with 4 normal stresses (13.5, 25, 50, and 100 KPa). It is concluded that the direct shear test, using cohesion and friction angle parameters, demonstrated the ability to adequately characterize the complex behavior of plastic mortars and the sensitivity to variations in the mixture. A linear correlation was found between the friction angle (shear test) and the consistency index (flow table), with R2 = 0,87. Furthermore, for high plasticity mortars, was found a non-linear correlation between compression flow (squeeze flow) and cohesion (direct shear test), with R2 = 0,67.

Mesoscale numerical modeling of unreinforced masonry wall response to underground dynamic loads: A comparative study utilizing FEM and DEM

This study investigates the response of unreinforced masonry walls to dynamic loading induced by underground explosions. A mesoscale numerical modeling approach is employed to capture the nonlinear behavior of the masonry wall. The Menetrey-Willam yield criterion is utilized to represent the wall's nonlinear behavior at the mesoscale level, while the cohesive zone model (CZM) is employed to simulate the behavior of mortar, thereby overcoming the limitations of linear elasticity. The soil is characterized using the modified Mohr-Coulomb model. After calibration against material characterization tests, a numerical model is developed to obtain results that closely match experimental data. Given the disturbed nature of the crater soil, both finite element and discrete element methods are utilized for soil modeling. Comparison between these methods reveals that the discrete element method yields more realistic results in terms of displacement and strain. The study's findings enhance our understanding of the response of unreinforced masonry walls to dynamic loading and offer valuable insights for future structural designs and safety assessments.

Underwater fatigue behavior of cementitious mortar and a countermeasure using a water-dispersible polyurethane ether–Portland cement composite

The underwater fatigue behaviors of cementitious mortars are investigated with a focus on the mechanisms contributing to the deterioration of bridge foundations and possible countermeasures. This study analyzes the effects of water penetration during repetitive loading and unloading on the underwater fatigue lives of cementitious materials, highlighting the importance of considering dynamic water motion, in addition to the surface energy mechanism. Water penetration during underwater fatigue occurs even in water-saturated specimens, and water in- and egress within a few millimeters of the specimen surface can significantly reduce the fatigue life. This study proposes a novel approach using a water-dispersible polyurethane ether–Portland cement composite as a countermeasure to improve underwater fatigue resistance. Based on experimental analysis of fatigue in water and microstructural investigations of the composite, the presence of polyurethane compounds within the nano-to-micron-sized microstructures may mitigate water penetration and contribute to a corresponding increase in underwater fatigue life.