Self-consolidating Mortar Research Articles

Mechanical properties and durability of self consolidating cementitious materials incorporating nano silica and silica fume

In recent years, the emergence of nanotechnology and nanomaterial has created hopes to improve various properties of concrete. Nano silica as one of these materials has been introduced as a cement replacement material for concrete mixture in construction applications. It can modify the properties of concrete, due to high pozzolanic reactions and also making a denser microstructure. On the other hand, it is well recognized that the use of mineral admixtures such as silica fume affects the mechanical properties and durability of cementitious materials. In addition, the superior performance of self-consolidating concrete (SCC) and self-consolidating mortars (SCM) over conventional concrete is generally related to their ingredients. This study investigates the effect of nano silica and silica fume on the compressive strength and chloride permeability of self-consolidating mortars. Tests include compressive strength, rapid chloride permeability test, water permeability, capillary water absorption, and surface electrical resistance, which carried out on twenty mortar mixtures containing zero to 6 percent of nano silica and silica fume. Results show that SCMs incorporating nano silica had higher compressive strength at various ages. In addition, results show that nano silica has enhanced the durability SCMs and reduced the chloride permeability.

Relationship between workability and mechanical properties of fibre-reinforced self-consolidating mortar

Non-uniform distribution of fibres and also instability of mixture tend to degrade as well as introduce undesirable variability into the mechanical properties of the mixture. This study investigates the effects of aspect ratio and volume fraction of polypropylene fibre on fluidity, flow time, stability and mechanical properties of fibre-reinforced self-consolidating mortars (FRSCMs). The obtained results indicate that stability and segregation resistance of ordinary self-consolidating mortars plays a significant role in the fluidity, stability and fibre dispersion of fibrous mortar. Moreover, this paper suggests critical and dense fibre factors to show the variability of fluidity, stability and also mechanical properties of mixtures. The results show that, for a water/cement ratio of 0·4 and fibre factor less than 90, fibres formed networks, in which aggregates are efficiently confined and so result in more segregation resistance of mixtures. On the other hand, for mixtures with a fibre factor above the dense fibre factor, non-uniform distribution and clumping of fibres occur, leading to a poor mechanical behaviour. The combined fluidity and stability data allow an improved description of the processes, which are responsible for segregation and fibre clustering in FRSCM.

Effect of Different Curing Regimes on Shrinkage and Strength Properties of Self-Consolidating Mortars Containing Silica Fume in Different Contents

The aim of this research is to study the effect of different curing regimes on shrinkage and strength properties of self-consolidating mortars (SCM) containing silica fume in different contents. Self-consolidating mortars, as new technology products, are especially preferred for use in architectural elements and the rehabilitation and repair of reinforced concrete structures. SCM can be used in precast architectural elements or cast in place repair of reinforced concrete structures. Therefore, investigation on the effects of different curing methods on key properties of SCMs can be beneficial. The shrinkage and strength properties of SCMs produced at different replacement ratios of silica fume (SF) with cement in different curing regimes were studied, at this paper. SCM mixes were prepared in constant water/powder ratio and cured in four different regimes including water curing (WC), accelerated water curing (AWC), air curing (AC) and aluminum tape sealing (AS). A polycarboxylate-based superplasticizer (SP) was added to the mixtures at different rates by mass of the cementitious materials to have appropriate flowability. Fresh mortars workability was determined using mini slump flow and mini V-funnel tests. All SCM specimens were tested and evaluated for compressive strength, flexural strength and shrinkage. It has been found that different curing regimes have considerable effects on both shrinkage and strength properties of SCM. It can be concluded that aluminum tape sealing and accelerated water curing can be used as effective and successful curing methods particularly where the SCM is used as a repair material or in architectural elements, respectively.

Effect of mineral admixtures on fluidity and stability of self-consolidating mortar subjected to prolonged mixing time

During continuous mixing of concrete in a truck mixer for its hauling to a construction site, concrete should remain workable without any signs of instability. Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties. This paper presents the effects of water to binder ratio, binary and ternary blends use of fly ash (FA) and metakaolin (MK) on fluidity, viscosity, and stability of self-consolidating mortars (SCMs) subjected to prolonged mixing time. The obtained results indicate that, by prolonged mixing time, flocculated cement particles are dispersed and as a result, fluidity is increased and so, the risk of instability increases. In addition, increasing FA content from 0 in the reference mixture to 20% and 50% of total binder mass increased the segregation index by about 48% and 160%, respectively. Furthermore, mixtures containing MK and FA have higher fluid capacity without any signs of instability. The addition of 7.5% MK has significantly improved the overall performance of the mixture, including the segregation stability.

Influence of mineral additive type on slump-flow and yield stress of self-consolidating mortar

Self-consolidating concrete flow mainly depends on the properties of the Self-consolidating mortar (SCM) design. SCM properties are influenced by mineral powder content, powder (mineral additive) type, and the chemical admixture content used in the mixes. In this study, the effects of mineral additives, the water/powder ratio, and the chemical admixture content on the yield stress of SCM was investigated. Five mineral additives, including limestone powder, waste marble powder, brick powder, fly ash, and limestone powder plus fly ash, were used. The SCM mixes with different powder types were prepared by using the polycarboxylate-based chemical admixture in ratios of 1, 1.5, 2 and 2.5% by powder weight. Total powder content (cement and mineral additives) was constant. The workability of fresh SCM was defined using the mini slump cone test and mini V-funnel tests. The yield stress of SCM was determined by the asymptotic flow regime approach, which depends on slump flow value. The test results show that the powder type is as effective as the chemical admixture and water/powder ratio (w/p) on the yield stress of SCM. SCM yield stress decreased as the w/p and SP dosage increased. Key words: Self-consolidating mortar, powder type, flow-ability, yield stress.

The role of scrap rubber particles on the drying shrinkage and mechanical properties of self-consolidating mortars

This study presents the results of an experimental investigation to study the effects of partial replacement of fine aggregate with scrap tire-rubber in self-consolidating mortar (SCM). Fresh and hardened properties of SCMs produced at five different replacement ratios of scrap rubber with sand, 0%, 10%, 20%, 30%, 40% and 50% (by weight of sand), were compared to those of without rubber. Mini slump flow and mini V-box flow time values were determined experimentally in fresh SCM. Moreover, drying shrinkage, apparent porosity, water absorption by weight, compressive and flexural strength, and dynamic modulus of elasticity were measured. While comparing the control SCMs, the partial replacement of scrap rubber with sand resulted in degradation in fresh and hardened properties. On the other hand, the addition of scrap rubber, from 10% to 40%, had a beneficial effect in decreasing the drying shrinkage of SCMs produced at low w/p (water-powder) ratios.

Relationship between fluidity and stability of self-consolidating mortar incorporating chemical and mineral admixtures

In this study, the effect of chemical and mineral admixtures, including superplasticizer, viscosity modifying agent (VMA), limestone powder and fly ash in different W/C on fluidity, viscosity, and stability of self-consolidating mortar is investigated and proper workability regions for the prepared mixtures are presented. The obtained results indicate that W/C is the most significant parameter influencing the rheological properties of cementitious mixtures, specially their stability. Furthermore, the maximum allowable W/C for preventing inhomogeneity could not be a fixed value for all the mixtures and should be adjusted for the target fluidity. On the other hand, using VMAs is an effective method for stabilizing self-consolidating mortars and preventing any kinds of instability while limestone powder and fly ash mainly affect bleeding and aggregate blockage. Besides, these mineral admixtures improved the fluidity of the mixtures to some extent.

Self-Consolidating Mortars Using Various Secondary Raw Materials

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