Showing papers on "Mortar published in 2013"

Use of waste glass as sand in mortar: Part I – Fresh, mechanical and durability properties

Abstract: In this study, mortar made with waste glass as fine aggregates was investigated for its suitability for construction use. A reference mortar mixture was proportioned according to ASTM C 109 and the fine aggregates were replaced by waste glass particles by 0%, 25%, 50%, 75% and 100%, by mass, to study its effect on the properties of mortar. For each mixture, four types of glass sand, namely, brown, green, clear and mixed color glass, were used. Test results indicated that use of waste glass particles as fine aggregates would reduce the flowability and density of mortar, but increase its air content. Except drying shrinkage, the mechanical properties were compromised due to micro-cracking in glass sand and weakened bond with the cement paste. However, durability was enhanced, especially in terms of the resistance to chloride ion penetration. Accelerated mortar bar tests to ASTM C 1260 indicated that green and brown glasses were non-reactive while clear glass was potentially deleterious, with regards to alkali–silica reaction.

Use of waste glass as sand in mortar: Part II – Alkali–silica reaction and mitigation methods

Abstract: Waste glass may be used in concrete provided that the potential deleterious expansion caused by alkali–silica reaction (ASR) could be mitigated. In this study, the influence of glass content, color and particle size on ASR expansion of mortar was determined by the accelerated mortar bar method. Two approaches to control ASR expansion were investigated for green, brown and clear glass sand mortar. They were: (1) by replacing cement with pozzolans, that is, 30% fly ash, 60% GGBS, 10% silica fume, or 20% glass powder; (2) by adding a suppressor, that is, plain steel fibers, and lithium chloride and lithium carbonate compounds. Test results showed that the ASR expansion increased with higher glass content in the case of clear glass sand mortar, but would decrease with increasing content for green and brown glass sand mortar. The ASR expansion also decreased with smaller glass particle size, regardless of glass color. Fly ash and GGBS were the most effective in mitigating ASR expansion, followed by silica fume, steel fibers and lithium compounds.

The effect of fiber properties on high performance alkali-activated slag/silica fume mortars

Abstract: The effects of length and volume fraction of steel fibers on the mechanical properties and drying shrinkage behavior of steel fiber reinforced alkali-activated slag/silica fume (AASS) mortars were investigated within the scope of this research. Steel fibers with two different lengths of 6 mm and 13 mm, and four different volume fractions of 0.5%, 1.0%, 1.5% and 2.0% were used in the AASS mixtures. Also, a Portland cement (PC) based 1.5% steel fiber (13 mm length) reinforced mortar was prepared for comparison. Test results showed that mechanical performance of AASS mortars were significantly better than PC based control mortar. This superior performance of AASS mortar may be attributed to the higher bond properties between the fibers and AASS matrix compared to PC matrix. The mechanical performance of AASS improved dramatically parallel to the increment of fiber length from 6 mm to 13 mm. Also, the drying shrinkage of AASS mortars decreased with the increasing fiber dosage.

Concrete mix design based on water film thickness and paste film thickness

Abstract: In previous studies on the mortar portion of concrete, it has been found that the water film thickness (WFT) and paste film thickness (PFT) have major effects on the performance of mortar. The present study aims to extend the concepts of WFT and PFT to concrete. For this aim, a number of concrete mixes with various paste volumes, water/cement ratios and fine to total aggregate ratios were produced for slump, flow, strength and packing density measurements, and from the results, the combined effects of WFT and PFT on the deformability, flowability and strength of concrete were studied. It was found that whilst the WFT is the key factor governing the above properties of concrete, the PFT also has significant effects and thus is an important factor to be considered in concrete mix design. Lastly, based on the test results, two design charts for concrete mix design were produced.

Crumb rubber aggregate coatings/pre-treatments and their effects on interfacial bonding, air entrapment and fracture toughness in self-compacting rubberised concrete (SCRC)

Abstract: The interfacial-bonding, interfacial transition zone (ITZ), and porosity are regarded as the key factors affecting hardened concrete properties. The aim of this study was to experimentally improve the bonding between the rubber aggregate and cement paste by different methodologies including water washing, Na(OH) pre-treatment, and both cement paste and mortar pre-coating. All methods were assessed by determining mechanical and dynamic properties, then correlating this with ITZ porosity and interfacial gap void geometry, along with quantification of the fracture energy during micro crack propagation using fractal analysis. The results indicated that pre-coating the rubber by mortar gave the best results in terms of fracture toughness and energy absorption showing good agreement between observations made at both micro and macro scales.

Using fine recycled concrete aggregate for mortar production

Abstract: This research assessed the performance of mortars in which recycled concrete aggregates (RCA) was a component. It replaced natural sand but kept the same particle size distribution. Three mortars were produced with replacement ratios of 20%, 50% and 100% as well as a reference mortar containing no recycled aggregate. The compressive and flexural strength, water absorption by capillarity, drying capacity and susceptibility to cracking of these mortars were analyzed first. Then, based on these results, the most satisfactory replacement ratio was chosen and the following properties were analyzed: water retentivity, shrinkage, adhesive strength, modulus of elasticity, and water vapor permeability. Somewhat surprisingly the best results in the first stage occurred for 20% and 100% replacement ratios, leading to a cautious choice of the 20% ratio for the second stage. Generally the mortar with 20% replacement ratio performed better than the reference mortar, except for adhesive strength and dimensional stability.

Production of nepheline/quartz ceramics from geopolymer mortars

Abstract: This research has investigated the mechanical properties and microstructure of metakaolin derived geopolymer mortars containing 50% by weight of silica sand, after exposure to temperatures up to 1200 °C. The compressive strength, porosity and microstructure of the geopolymer mortar samples were not significantly affected by temperatures up to 800 °C. Nepheline (NaAlSiO4) and carnegieite (NaAlSiO4) form at 900 °C in the geopolymer phase and after exposure to 1000 °C the mortar samples were transformed into polycrystalline nepheline/quartz ceramics with relatively high compressive strength (∼275 MPa) and high Vickers hardness (∼350 HV). Between 1000 and 1200 °C the samples soften with gas evolution causing the formation of closed porosity that reduced sample density and limited the mechanical properties.

Mechanical performance and durability of treated palm fiber reinforced mortars

Abstract: The performance of cement mortar reinforced with varying percentages of treated bundled date palm fibers is investigated to appraise their feasibility for structural and non-structural applications. The study first entailed the evaluation of two different alkali pre-treatments at varying concentrations by subjecting treated and untreated bundled fibers to tensile testing. The suitable pre-treatment was then adopted while casting cement mortar mixes. The physical properties of fresh mortar was studied through setting times and, for mortar mixes cured up to 28 days, through parameters such as drying shrinkage and water absorption. The unconfined compressive strengths, split tensile strengths as well as the flexural strengths of the cured mortar mixes at two different ages were undertaken to assess their mechanical properties; while the durability was gauged based on their sulfate resistance for up to a period of four months. Observed stress–strain behavior under tension led to the choice of 0.173% Ca(OH) 2 as the preferred pre-treatment for the bundled fibers used in the mortar mixes. This was further supported by the microstructural examination on the hardened mortars which, revealed that the integrity of treated fibers remained intact within the cement matrix without hindering the hydration processes. Results also indicated that inclusion of fibers improves the flexural strengths as well as the sulfate resistance of the mortar mixes. However, the cylinder and cube compressive strengths decreased with the increase in treated fiber inclusion. Although, the work reported in this paper was carried out on cement mortars, conclusions are expected to be relevant to fiber reinforced concrete employing treated natural fibers.

Mechanical Properties and Microstructure of Class C Fly Ash-Based Geopolymer Paste and Mortar.

Abstract: This paper presents workability, compressive strength and microstructure for geopolymer pastes and mortars made of class C fly ash at mass ratios of water-to-fly ash from 0.30 to 0.35. Fluidity was in the range of 145–173 mm for pastes and 131–136 mm for mortars. The highest strengths of paste and mortar were 58 MPa and 85 MPa when they were cured at 70 °C for 24 h. In XRD patterns, unreacted quartz and some reacted product were observed. SEM examination indicated that reacted product has formed and covered the unreacted particles in the paste and mortar that were consistent with their high strength.

On the use of R-PET strips for the reinforcement of cement mortars

Abstract: We study the alkali resistance and the flexural response of a cement-based mortar reinforced through polyethylene terephthalate (PET) strips obtained through hand cutting of ordinary post-consumer bottles. On considering 1% fiber volume ratio and different strip geometries, we show that the analyzed reinforcing strips owe remarkable alkali resistance and are able to markedly improve the toughness of the base material. Comparisons are established with the outcomes of a recent study on a similar reinforcement technique of a cement–lime mortar.