Showing papers on "Mortar published in 2017"

Waste glass powder as partial replacement of cement for sustainable concrete practice

Abstract: Million tons of waste glass is being generated annually all over the world. Once the glass becomes a waste it is disposed as landfills, which is unsustainable as this does not decompose in the environment. Glass is principally composed of silica. Use of milled (ground) waste glass in concrete as partial replacement of cement could be an important step toward development of sustainable (environmentally friendly, energy-efficient and economical) infrastructure systems. When waste glass is milled down to micro size particles, it is expected to undergo pozzolanic reactions with cement hydrates, forming secondary Calcium Silicate Hydrate (C–S–H). In this research chemical properties of both clear and colored glass were evaluated. Chemical analysis of glass and cement samples was determined using X-ray fluorescence (XRF) technique and found minor differences in composition between clear and colored glasses. Flow and compressive strength tests on mortar and concrete were carried out by adding 0–25% ground glass in which water to binder (cement + glass) ratio is kept the same for all replacement levels. With increase in glass addition mortar flow was slightly increased while a minor effect on concrete workability was noted. To evaluate the packing and pozzolanic effects, further tests were also conducted with same mix details and 1% super plasticizing admixture dose (by weight of cement) and generally found an increase in compressive strength of mortars with admixture. As with mortar, concrete cube samples were prepared and tested for strength (until 1 year curing). The compressive strength test results indicated that recycled glass mortar and concrete gave better strength compared to control samples. A 20% replacement of cement with waste glass was found convincing considering cost and the environment.

Improving flexural performance of ultra-high-performance concrete by rheology control of suspending mortar

Abstract: This study develops a rheology control method to improve steel fiber distribution and flexural performance of ultra-high-performance concrete (UHPC) by adjusting the rheological properties of the suspending mortar of UHPC before steel fibers are added. Correlations among the plastic viscosity of the suspending mortar, the resulting steel fiber distribution, and flexural properties of UHPC are established. This was done by changing the dosage of viscosity modified admixture (VMA) for investigated UHPC mixtures. The optimal plastic viscosity of the suspending mortar that allows for the optimized fiber distribution and flexural performance of UHPC is determined. The plastic viscosity is correlated with the mini V-funnel flow time, which provides a simple alternative to evaluate the plastic viscosity. For a UHPC mixture with 2% micro steel fibers, by volume, the optimal mini V-funnel flow time of suspending motar was determined to be 46 ± 2 s, which corresponded to the optimal plastic viscosity (53 ± 3 Pa s) that ensures the greatest fiber dispersion uniformity and flexural performance of UHPC. However, increasing the VMA dosage retarded the hydration kinetics and reduced the degree of hydration, compressive strength, and the bond properties of the fiber-matrix interface of UHPC.

Round Robin Test on tensile and bond behaviour of Steel Reinforced Grout systems

Abstract: Mortar-based reinforcements are an innovative solution for retrofitting existing structures that combine effectiveness, compatibility, and sustainability. Despite the recent spreading of field applications, there is still insufficient knowledge on their fundamental mechanical properties, and a regulatory gap for experimental procedures and design criteria. A Round Robin Test initiative was organized by the Rilem TC 250-CSM (Composites for the Sustainable strengthening of Masonry) to investigate the tensile and bond behaviour of mortar-based composites with basalt, carbon, glass, polyparaphenylene benzobisoxazole (PBO), aramid and steel textiles. This paper presents the tests carried out on Steel Reinforced Grout (SRG) systems, comprising three textile and four mortar types, supplied by three producers. Ten laboratories from Italy, Poland and Portugal were involved for a total of 150 tests, including direct tensile tests on textiles and composites, and single-lap bond tests on masonry substrate. The influence of the layout of the textile, the mechanical properties of the mortar matrix, the manufacturing and curing conditions, as well as the testing setup and instrumentation, is discussed to contribute to the optimization of the reinforcement systems and to the development of recommendations for laboratory testing. Finally, results are combined to derive engineering parameters for qualification and design purposes.

Effect of self-healing on strength and durability of zeolite-immobilized bacterial cementitious mortar composites

Abstract: There is a compelling economic incentive to develop concrete materials that can repair its own damage, increase durability and prevent structural failure This research investigated the potential of adding two different mineral producing bacteria into two types of cementitious mortar matrix to enhance self-healing ability for autonomous crack repair In this study, zeolite was used as a carrier material to protect bacteria in high pH environment normally exists in concrete The spore forming ability and ureolytic activity of zeolite-immobilized bacteria were investigated in order to examine potential for producing healing compounds The self-healing ability of bacteria incorporated normal and fiber reinforced mortars was judged based on the development of compressive strength and permeation properties of cracked specimens with age as well as micro-structural characterization of crack healing compounds using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction

Test methods for Textile Reinforced Mortar systems

Abstract: Textile Reinforced Mortar (TRM) composites, also named Fabric Reinforced Cementitious Matrix (FRCM), comprise high strength textiles embedded into inorganic matrices, and have been recently developed for the repair and rehabilitation of structures. Their effectiveness and compatibility with the substrate fostered the industrial development of a wide number of strengthening systems, which have been applied to masonry and reinforced concrete structures. Nevertheless, an improved knowledge still needs to be gained on their mechanical properties (tensile and bond behaviour) and on the effect they have on the structural performance of reinforced members. Furthermore, except for the US, no standards are available for testing, qualification and design. In this paper, the main features of the tensile and bond behaviour of TRM composites are described. Recommendations for performing direct tensile tests and shear bond tests are proposed, based on the outcomes of a Round Robin Test organized by the Rilem TC 250-CSM (Composites for the Sustainable strengthening of Masonry) and Assocompositi (Italian Industry Association for Composite Materials), carried out on 26 TRM systems (made of basalt, carbon, steel, glass, PBO and aramid textiles, with cement, lime or geopolymer mortar matrices), and involving 19 European research institutions and 11 industrial partners.

Monitoring Concrete Deterioration Due to Reinforcement Corrosion by Integrating Acoustic Emission and FBG Strain Measurements

Abstract: Corrosion of concrete reinforcement members has been recognized as a predominant structural deterioration mechanism for steel reinforced concrete structures. Many corrosion detection techniques have been developed for reinforced concrete structures, but a dependable one is more than desired. Acoustic emission technique and fiber optic sensing have emerged as new tools in the field of structural health monitoring. In this paper, we present the results of an experimental investigation on corrosion monitoring of a steel reinforced mortar block through combined acoustic emission and fiber Bragg grating strain measurement. Constant current was applied to the mortar block in order to induce accelerated corrosion. The monitoring process has two aspects: corrosion initiation and crack propagation. Propagation of cracks can be captured through corresponding acoustic emission whereas the mortar expansion due to the generation of corrosion products will be monitored by fiber Bragg grating strain sensors. The results demonstrate that the acoustic emission sources comes from three different types, namely, evolution of hydrogen bubbles, generation of corrosion products and crack propagation. Their corresponding properties are also discussed. The results also show a good correlation between acoustic emission activity and expansive strain measured on the specimen surface.

Mortar crack repair using microbial induced calcite precipitation method

Abstract: An experimental investigation has been carried out to repair pre-existing cracks in mortar using the microbiologically induced calcium carbonate precipitation (MICP) technology. In the study, 20 cylinder mortar samples (50 mm in diameter and 40 mm in height) were split to have cracks with various sizes. Sixteen of the cracked samples, an average width ranging from 0.15 to 1.64 mm, were repaired using the MICP method, while four cracked samples, with an average width ranging from 0.17 to 1.72 mm, were soaked under distilled water. The water permeability and splitting tensile strength (TS) of these repaired mortars were tested. The amounts of calcium carbonate (CaCO 3 ) precipitated on the cracked mortar surfaces were evaluated. The morphology of the CaCO 3 was observed under a scanning electron microscope (SEM). The results indicated that the MICP repair technique clearly reduced water permeability of the cracked samples. While water-treated samples were too weak to test, the MICP-repaired samples had TS ranging from 32 to 386 kPa after 21 cycles of MICP solution treatment. A relationship between the TS and amount of CaCO 3 precipitated was observed for samples with an average crack width between 0.52 and 1.1 mm, which indicated that TS increased with the amount of CaCO 3 precipitated on the crack surfaces. The SEM revealed that the precipitated CaCO 3 had possibly two forms: vaterite and calcite.

Tensile behaviour of a basalt TRM strengthening system: Influence of mortar and reinforcing textile ratios

Abstract: The use of textile reinforced mortar (TRM) composites is considered a suitable solution to strengthen historical masonry structures. Specifically, TRM composites are characterised by a textile embedded in a mortar matrix. In the present work, we propose a thorough experimental analysis of basalt textile reinforced mortar. Four series of tensile tests were carried out on specimens characterised by three different basalt textile reinforcing ratio and two different kinds of mortar (usual gauged mortar and thixotropic mortar with additives). The use of digital image correlation facilitated detailed description of the displacement fields and the crack pattern during the tests. The comparison between the results of each series allowed us to evaluate the influence of the different parameters on the behaviour of the analysed TRM and to obtain useful information regarding the strengthening design.

Bond strength between concrete substrate and metakaolin geopolymer repair mortar: Effect of curing regime and PVA fiber reinforcement

Abstract: The suitability of repairing Portland cement concrete with geopolymer mortars is explored as a viable way to replace Portland cement in concrete repairs and reduce their carbon footprint. Bond tests are performed through non-standard slant shear tests with variable bond plane inclination to assess concrete-geopolymer shear bond strength under different combinations of normal and shear stresses at the concrete-geopolymer interface. Interfacial cohesion and friction coefficients, two inherent mechanical properties of the substrate-repair interface, are extrapolated from experimental data and compared among different types of geopolymer repairs. The adoption of different curing temperatures for the geopolymer repair mortar (20°C and 45°C) and its reinforcement with various contents of Polyvinyl Alcohol fibers (volume fractions Vf = 0%, 0.5%, and 1%) are investigated to optimize the substrate-repair bond. Mechanical tests are supported by statistical analysis and microscope observation.

Mechanical properties and durability of mortar containing fine fraction of demolition wastes produced by selective demolition in South Italy

Abstract: Recycling of construction and demolition waste (CDW) has to be encouraged. Structural concrete and mortar is one of the possible applications, but requires a good quality of the aggregates to be used.The use of wastes treated by mobile plants in the above application is possible only if an accurate selective demolition is conducted. The goal of this study is to produce self-levelling mortars containing high amount of CDW fine fractions that are problematic waste materials. This research investigate the physical and mechanical characteristics of different kind of CDW obtained from selective and traditional demolition techniques. Comparison between the properties of the mixtures obtained from different kind of aggregates offers the possibility to understand the advantages in using selective demolition. The results show that the use of superplasticizer, combined with selective demolition, can improve significantly the mechanical properties of mortars produced with CDW aggregate. In particular aggregate coming from bricks can improve mechanical strength, probably because of their pozzolanic effect.

Combined use of waste glass powder and cullet in architectural mortar

Abstract: The use of 100% waste glass cullet (WGC) as fine aggregates in architectural cement-based mortar had been proven to be feasible in previous works. This paper reports a further study on investigating the influence of using waste glass powder (WGP) as a supplementary cementitious material on the properties of glass-based architectural cement mortars. The experimental results showed a good linear relationship between the particle size of WGP and the flow values of the fresh mortar, revealing that the particle size of WGP played an important role in controlling the workability. For the hydration of white cement, the inclusion of WGP not only affected the second exothermic peak of hydration but also changed the third peak. In particular, the result indicated that the use of finer WGP had an advantage in increasing the flexural strength of the cement mortar when compared with the corresponding compressive strength, which was attributed to the morphological and pozzolanic effect of WGP. In addition, the very fine WGP could act as micro-fibers and micro-aggregates in filling the microstructure of the mortar. At 90 days of curing, the mortar prepared with finer WGP showed a distinct improvement in strength due to the improved interfacial transition zone and the pore-size refinement.