High Strength Mortar Research Articles

Mechanical properties and microstructure of recycled mortar reinforced with hybrid fiber

This study investigated the hybrid effects of two types of microfiber, namely, polypropylene and nylon, on the mechanical properties of high-strength mortar, which produced fine recycled aggregate (FRA). The amount of microfibers was maintained at a volumetric fraction of 0.6%. The microstructure and mechanical strength properties (compressive strength and flexural strength) of recycled mortar reinforced with hybrid-size microfibers were evaluated at various curing ages. Experimental results show that the inclusion of hybrid fibers significantly influenced the mechanical performance of the recycled mortar. The hybridization fiber at volume fraction 0.3% polypropylene + 0.3% nylon yielded the most promising mechanical performance. Enhancements of 8% on compressive and 11% flexural strength were achieved at 28 days. Scanning electron microscopy observations revealed that reinforcement at the microscale prohibited the initiation and growth of cracks at the micro level. High loads were required to form macrocracks within composites, thereby improving the mechanical strength of the mortar matrix.

Flexural behaviors of fiber-reinforced polymer fabric reinforced ultra-high-performance concrete panels

The use of fiber-reinforced polymer (FRP) fabrics as reinforcement in concrete offers several advantages, such as high tensile strength, corrosion resistance, and light weight. This paper presents experimental and mechanical studies on the flexural behaviors of FRP fabric reinforced ultra-high-performance concrete (UHPC) panels. Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) fabrics were investigated. Mechanical properties of GFRP and CFRP fabrics, high-strength mortar, and UHPC containing micro steel fibers were experimentally evaluated. The interfacial properties between the FRP fabric and cementitious matrix were characterized using push-pull tests. The flexural performance of panels with different reinforcement configurations was experimentally evaluated. The use of GFRP or CFRP fabric enhanced the flexural properties of UHPC panels, but did not lead to any increase in the flexural strength for the panels made with high-strength mortar. A mechanical analysis is performed to understand and predict the flexural behavior of the FRP fabric reinforced UHPC panels. The proposed fabric reinforced UHPC panel is demonstrated to be promising for the development of lightweight, high-performance permanent formwork system. Such formwork can be potentially used in accelerated construction of critical infrastructure with enhanced crack resistance and extended service life.

Seismic performance of precast composite shear walls reinforced by concrete-filled steel tubes

A type of precast slender composite shear wall was proposed and experimentally studied. In this new precast structural wall system, concrete-filled steel tubes (CFSTs) were used to entirely replace the longitudinal reinforcement in the boundary elements of conventional reinforced concrete (RC) shear walls. At joints, the CFSTs and wall web reinforcement were connected by sleeves filled with high-strength mortar. To examine the seismic performance of the proposed system, seven 1/3-scale specimens were built and tested under quasi-static and dynamic cyclic lateral loading with a top displacement rate up to 20 mm/s. Major test variables included axial force ratio ranging from 0.075 to 0.19 and loading rate. This paper reports the damage pattern, hysteretic load-deformation response, energy dissipation capacity, and connection performance of the test specimens. Under the considered axial force levels and loading rates, lateral loads were successfully resisted at the joints and the response of all specimens was dominated by flexure. The use of CFSTs increased lateral strength and deformation capacity. The highest axial force ratio caused drift capacity to be reduced from 2.5% to 2.0%. Although loading rate nearly had no influence on either lateral stiffness or strength, it reduced energy dissipation capacity. Finally, the effectiveness of proposed detailing of sleeve-mortar connections in load transfer was validated by the similar hysteric response, joint opening, and wall sliding between monolithic and precast CFST wall specimens.

Mechanical Properties of High Strength Mortars Made withFine Waste Concrete Aggregates and Ground Granulated Blast Furnace Slag

The mechanical properties of high strength mortars produced with fine waste concrete aggregate (FWCA) and GGBFS were investigated. The natural sand was replaced by FWCA with different levels, namely 0, 25, 50, 75, and 100%. The ordinary Portland cement (OPC) was substituted by GGBFS with 0, 30, and 60% by weight. To satisfy the requirements of high strength, all the mortar mixes were made with a 0.25 w/bratio. The hardened mortars were tested for compressive strength, splitting tension, and fracture parametersat different ages.The experimental findings showed that the mixtures with FWCA showed lower strength, fracture energy and toughness compared to the corresponding reference mixes at a given age and GGBFS content. The 30% replacement of OPC by GGBFS improved the strengths of all mixes at 28 and 90 days. Moreover, the use of 30% GGBFS counterbalanced the strength decrement due to the use of the FWCA such that the mixtures with FWCA and GGBFS showed strengths comparable to or even exceeded the strengths of the mixtures made with natural sand only.

Experimental diagonal tension (shear) test of Un-Reinforced Masonry (URM) walls strengthened with textile reinforced mortar (TRM)

The presented study is part of ongoing experimental program on Un-Reinforced Masonry (URM) walls strengthened with Textile reinforced mortars (TRM). Ten walls were tested under diagonal tension (shear) test method in order to consider the effect of strengthening system on the behavior of brick walls. One plain wall was tested as reference. Two walls were overlaid with 15 and 25 mm thick of high strength mortar on one face without any textile sheet. Another seven walls were externally strengthened with 15 and 25 mm thick of AR-Glass Textile Reinforced Mortar (TRM) on one or both faces. Results confirmed the efficient possibility of shear strengthening of existing URM walls using TRM, especially for those strengthened on both faces. On the other hand, one face strengthened walls were sensitive to the applied load and can buckle or experience out-of-plane deformations. TRM extremely improved diagonal load carrying capacity and deformation capacity, which caused the strengthened walls fail in a ductile manner. The governing failure mode was out-of-plane deformation for one face strengthened walls, and failure of both faces strengthened walls was controlled by initiation of substrate toe crushing in compression continued by diagonal crashing. Results showed that for masonry walls strengthened on both faces, during pure in-plane diagonal load, there is no need to mechanical connection between TRM and masonry substrate. However, out-of-plane failure is an important issue for masonry walls, especially for those strengthened on one face. Therefore, connectors must be designed for out-of-plane lateral force to ensure that masonry wall and TRM reinforcement layer work together properly.

Volumechange and strength characteristics of normal and high-strength mortars: effect of aggregate type and water-binder ratio

AbstractThis study investigated the impact of aggregate type on the volume changes including drying shrinkage, autogenous shrinkage, and swelling for mortars made with different w/b ratios. The main properties including compressive and flexural strengths were also studied. For this purpose, three groups of mixes were prepared: two of them were prepared with 0.2 and 0.3 w/b ratios which were classified as high-strength mortars, and for comparison, a one group of normal-strength mortars was prepared with a 0.5 w/c ratio. Each group consisted of three mixes made with natural sand (NS), limestone aggregate (LA), or recycled concrete aggregate (RCA). Within each group, the LA mixes generally showed the lowest drying shrinkage and autogenous shrinkage regardless of the w/b ratio, while the greatest ones were observed for RCA mortars. The results also indicated that the group of mixes of the 0.2 w/b ratio gave the highest autogenous shrinkage.

Influence of Curing Methods on Compressive Strength and Shrinkage of High Strength Mortar with High Volume SCMs

Influence of Curing Methods on Compressive Strength and Shrinkage of High Strength Mortar with High Volume SCMs

Effect of chloride content on mechanical properties of ultra high performance concrete

Experimental results on the effects of chloride content of ultra high performance concrete (UHPC) are presented. The experimental variables are the amount of sodium chloride, ranging from zero to 3.0% per cement weight, and matrix strength, including normal mortar and high strength mortar. Sodium chloride is directly mixed with cement matrix in order to simulate harsh environments by promoting the corrosions of fibers and matrix. The effects of chloride content are evaluated in terms of visual observation, electrical resistivity change, compressive strength, bending strength, and dynamic Young's modulus. The experimental results show that UHPC has the superior capability to resist chloride ions due to its dense microstructures, which prevent the growth of rust crystals. Furthermore, the experimental findings suggest that the potentials for corrosion of steel fibers and for corrosion-induced matrix cracking are inconsequential in UHPC even if chloride ions penetrate into UHPC.

A Novel Method for Measuring Porosity for Normal and High Strength Concrete

Abstract This paper described a novel apparatus for the measurement of porosity for normal and high strength mortar and concrete using vacuum-pressure saturation method. A detailed description of design, test procedure, and evaluation of results of the vacuum-pressure saturation apparatus was presented. Porosity values obtained using the apparatus were highly repeatable and reproducible. The apparatus could detect the effect of age, influence of water-binder ratio, and influence of supplementary cementitious materials of concrete and mortar mixtures. The apparatus yielded full saturation for high strength and dense mortar and concrete. The porosity values for normal strength concrete using the vacuum-pressure saturation apparatus were in good agreement with the results obtained using vacuum saturation method proposed by RILEM.

Critical parameters for the compressive strength of high-strength concrete

This study investigates the influence of several material properties underlying the failure mechanism of high-strength concrete (HSC) under uniaxial compression. An experimental-numerical characterization of a single inclusion block (SIB) – an idealized composite comprising of a granite cylindrical core embedded within a high-strength mortar (HSM) matrix – is first carried out. Parametric studies are next conducted with the calibrated SIB model, to identify the critical parameters governing the failure of the idealized composite. The qualitative understanding obtained from the SIB is then utilized to design a series of experiments, exploring the extent of influence of the identified critical parameters on the compressive strength of HSC. Complementary experimental data in literature are also examined. For the range of specimens considered, it is found that the lateral strain capacity of mortar matrix has the most influence on the compressive strength of HSC.

Study on out-of-plane behaviour of unreinforced masonry strengthened with welded wire mesh and mortar

Unreinforced masonry (URM) is the oldest construction technique. URM being brittle cannot withstand the lateral loads during earthquake, hence it is necessary to find a suitable cost effective technique to strengthen masonry buildings in order to resist earthquake loads without causing any damage to life. In this paper, an attempt has been made to strengthen the URM samples of high strength mortar (1 cement : 4 sand) and low strength mortar (1 cement : 6 sand) which are commonly used in Indian construction practice, using mortar (1 cement : 3 coarse sand) and welded wire mesh (WWM) of various spacing (25mm, 38mm, 50mm) which are locally available in market. A series of 6 URM panels and 18 reinforced masonry panels have been tested under three-point loading method as per ASTM E518-10 recommendations to study the out-of-plane behaviour of both URM and WWM mortar reinforced masonry. The mode of failure and behaviour of masonry have been investigated in terms of strength, stiffness and ductility. The results show that strengthening of masonry using WWM enhanced the flexural strength and ductility of masonry.

Predicting the drying shrinkage behavior of high strength portland cement mortar under the combined influence of fine aggregate and steel micro fiber

The workability, 28-day compressive strength and free drying shrinkage of a very high strength (121-142 MPa) steel micro fiber reinforced portland cement mortar were studied under a combined influence of fine aggregate content and fiber content. The test results showed that an increase in the fine aggregate content resulted in decreases in the workability, 28-day compressive strength and drying shrinkage of mortar at a fixed fiber content. An increase in the fiber content resulted in decreases in the workability and drying shrinkage of mortar, but an increase in the 28-day compressive strength of mortar at a fixed fine aggregate content. The modified Gardner model most accurately predicted the drying shrinkage development of the high strength mortars, followed by the Ross model and the ACI 209R-92 model. The Gardner model gave the least accurate prediction for it was developed based on a database of normal strength concrete.

An Experimental Study on Fatigue Strength of Pile to Sleeve Grouted Connection using High Strength Mortar

An Experimental Study on Fatigue Strength of Pile to Sleeve Grouted Connection using High Strength Mortar

Mix Proportions of High Flowable Early Strength Mortar for Emergency Repair of Damaged Road Base in Rural Area

Recently, due to the climate changes, the frequency and severity of natural disasters such as torrential rain have become more significant worldwide. In South Korea, there are number of summer typhoons and localized torrential downpour every year and these cause severe damages onto a residential area and road networks. More than 70% of the land of Korean peninsula is a mountainous area and thus damages onto road networks result in serious harm to daily lives especially in a rural area by isolating residents from networks. Therefore, there is a strong demand on the immediate and emergency repair technology for the collapsed road networks. This study develops an emergency repair technique for damaged road base where the damaged road base can be packed with gravels and then the pores or open-gaps of the packed gravels can be filled with high flowable mortar that develops strength in an early age. The aim of this research study was to find the suitable mix proportions of high flowable early strength mortar. Throughout the experimental work, study was done on two stage mix variables, where in the 1st stage, W/C ratio and high range water reducer was considered whereas in the 2nd stage cost effective early strength cement was used for the mix-design. With various variables in mix proportions, compressive strength and flow capacity were investigated. Finally from those experimental study, optimum mix proportions of the high flowable early strength mortar was found. The hardened materials composited with gravels and mortars can be used as a permanent road base with no need for compaction thereafter.

Effects of silanes and silane derivatives on cement hydration and mechanical properties of mortars

An experimental research was conducted with the objectives to study the effects silanes (amino, vinyl, and epoxy-based) and their derivatives (silane oligomers and silane nanoparticles) on cement hydration and mechanical properties of mortars. Silanes and silane derivatives are used as coupling agents to combine different compositions in mortars and to chemically react with calcium silicate hydrates to introduce organic component into CSH structure. The use of silanes retarded the cement hydration. However, silane derivatives were found to effectively mitigate the retardation. Liquid-state 29Si nuclear magnetic resonance (NMR) spectroscopy indicated that silanes and silane derivatives have different hydrolysis and condensation products in the solutions of cement pastes. Further analysis of silicon concentration in the solution indicated that the hydrolysis and condensation products of silane oligomer is opt to be in the solution, instead of adsorption onto the surface of cement hydration products, to retard the cement hydration.Ordinary mortars with the silanes and silane derivatives showed general enhancement in flexural strength and some improvement in compressive strength after curing for 7days and 28days. Due to good strength properties, negligible hydration retardation, and simple preparation method, epoxy-based silane oligomer was selected for further study in high-strength mortar. Results indicated that the compressive strength, splitting tensile strength, and elastic modulus of the high-strength mortar were increased by 20%, 38%, and 13%, respectively, compared with the control mortar.

Internal-curing efficiency of cold-bonded coal bottom ash aggregate for high-strength mortar

Herein is reported the results of a study on the internal-curing efficiency of cold-bonded bottom ash aggregates (CBBA) used in high-strength mortar. The flow and compressive strength of high-strength mortar with CBBA were measured. To evaluate the internal curing efficiency of CBBA, the autogenous deformation and internal relative humidity of mortar with pre-wetted CBBA were observed at an early age. In addition, the degree of hydration was measured, and then differential thermal and thermogravimetric analyses (DTA/TGA) were carried out to understand the hydration kinetics of the mortar. The experimental results of mortar with CBBA were compared with those of mortar with raw bottom ash, and with artificial lightweight aggregates. Compared with raw bottom ash, CBBA showed greater mitigation of autogenous shrinkage, meaning that a lower volume proportion of CBBA was sufficient to eliminate autogenous shrinkage in the high-strength mortar.

Experimental investigation of compressive failure in masonry brick assemblages made with soft brick

An experimental investigation of compressive failure in masonry made of soft clay bricks is presented. Masonry assemblages are tested to evaluate the influence of the relative strength of mortar on the observed damage evolution and compressive failure. Damage evolution associated with the formation and propagation of vertical splitting cracks during the compressive load response of masonry assemblages in the stack bonded arrangement are studied using a full-field optical technique based on digital image correlation. Using image correlation, clear evidence of the crack forming in the mortar and propagating into the brick is established. Damage is associated with cracking in the mortar due to lateral tension produced by the confined expansion of brick. Failure depends upon the tensile strength of the mortar. In mortar with lower strength than the brick unit, failure is produced by spalling associated with multiple cracks, which results in a loss of load bearing area. For mortar with a higher strength than the brick, cracking occurs when the level of compression is a significant proportion of the compressive strength of the brick material. Localized crushing resulting from localization of strain in a small region at the brick–mortar interface is produced at axial stress close to the unconfined compressive strength of the brick material. Failure in the case of high strength mortar is a result of the localized crushing and the resulting global instability.

Reusable and recyclable nonbonded composite tapes and ropes for concrete columns confinement

Abstract This paper investigates the use and efficiency of structural continuous tapes (laminates), fibre tapes and fibre ropes made of different materials (natural or not) in enhancing the axial strain ductility and stress of confined concrete. All used confining materials are non-impregnated, unbonded to concrete and thus easy to reuse and recycle. Concrete cylinders confined with polypropylene rope reached axial strain as high as 0.15 with no rope fracture. Wrapping of cylinders with ultra-high molecular weight polyethylene (UHMWPE) tape or aramid fibre tapes or basalt fibre tapes may provide concrete significantly enhanced mechanical properties under monotonic or cyclic load. Cylinders wrapped with basalt fiber tape presented gradual fibre fracture and ductile load drop after maximum bearing load. Vinylon fibre ropes and UHMWPE or basalt or aramid fibre tapes show interesting resilience features as they can reach high portion of their confining efficiency even after their fracture initiation. In addition, the study presents the test results of severely damaged reinforced concrete (RC) column, repaired with high strength mortar and externally wrapped with hybrid basalt – polypropylene confinement. The retrofitted column fully restored the original ever-increasing σ-e behavior, revealing remarkable energy dissipation under cyclic loading. It reached 0.052 axial strain and then it was early terminated for safety reasons, despite having already sustained 0.058 strain during initial loading.

하이브리드 섬유를 혼입한 고강도 모르타르의 역학적 특성에 관한 연구

하이브리드 섬유를 혼입한 고강도 모르타르의 역학적 특성에 관한 연구

Repair Mortar for Structural Sustainability

Objectives: Study on the engineering properties of fiber reinforced polymer cement mortar with incremental replacement of cement by silica fume, Granulated Blast Furnace Slag (GGBS) and Metakaoline (MK). Methods/Statistical Analysis: Cement is replaced by the additives as 5, 10 and 15 percent by weight. Polymer content (SBR) was varied as 5, 10, 15 and 20 percent by weight of water to be added. The FRP fiber addition is optimized to one percent by weight of cement in all the specimens. The intention was to study the variation in engineering properties of fiber reinforced polymer with additive replacement of binder with the additives and water with polymer. Findings: It is concluded from the test results that the compressive and flexural strength of modified mortar were improved markedly with increasing polymer binder ratio and also additive replacement of binder weight by silica fume, GGBS and Metakaoline. The results obtained has given much higher values when compared to individual addition of additives or polymer. The consistency in values of both compressive and flexural strength marks the much higher efficiency of the mortar even in lower percentage of addition of additive or polymer when added individually. Supplementary Cementing Materials (SCM) have growing importance in the construction industry, as it upgrades the economic and engineering efficiency of cement compositions. The replacement of water with polymer reduces the water binder ratio, driving to high strength and durable repair mortars. The polyester fibers addition resulted in the improvement of the mechanical properties of the composition. Applications/Improvements: Thus the fiber reinforced mortar combination is a mark in structural sustainability of not only modern but also for structural rehabilitation of historic monuments, where it can replace the ancient lime mortars with high strength and durability hand in hand.