The Efficacy of Accelerated Test Methods to Evaluate Alkali Silica Reactivity of Recycled Concrete Aggregates

The effectiveness of accelerated tests in evaluating the Alkali-Silica Reactivity of Recycled Concrete Aggregates was evaluated. The Accelerated Mortar Bar Test was found effective for evaluating potential alkali-reactivity when the test variables, such as crushing method and absorption, are carried out in a well-defined process. The method of crushing was found to have significant impact on the expansion. The Concrete Microbar Test (CMBT) provides good correlation to the expansion of Concrete Prisms incorporating Supplementary Cementing Materials when an expansion limit of 0.10% at 56 days or 0.04% at 28 days were used, based on the limited number of tests carried out here.

The Efficacy of Accelerated Test Methods to Evaluate Alkali Silica Reactivity of Recycled Concrete Aggregates

The effectiveness of accelerated tests in evaluating the Alkali-Silica Reactivity of Recycled Concrete Aggregates was evaluated. The Accelerated Mortar Bar Test was found effective for evaluating potential alkali-reactivity when the test variables, such as crushing method and absorption, are carried out in a well-defined process. The method of crushing was found to have significant impact on the expansion. The Concrete Microbar Test (CMBT) provides good correlation to the expansion of Concrete Prisms incorporating Supplementary Cementing Materials when an expansion limit of 0.10% at 56 days or 0.04% at 28 days were used, based on the limited number of tests carried out here.

Effect of sample geometry and aggregate type on expansion due to alkali-silica reaction

Late expansions due to alkali-silica reaction were observed in field samples for some aggregates and supplementary cementing materials (SCM) combinations despite meeting the 2-year expansion criterion of the concrete prism test. This fosters a research into the effect of sample geometry and aggregate reactivity on alkali leaching and expansion of lab samples. Larger samples showed less leaching compared to standard prisms. Cylinders of 100 mm-diameter showed higher expansion than 75 mm-standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. Alkali leaching from concrete samples and alkali release from some aggregates could lead to cylindrical samples having higher expansion and better correlation to field samples compared to standard concrete prisms.

Effect of sample geometry and aggregate type on expansion due to alkali-silica reaction

Late expansions due to alkali-silica reaction were observed in field samples for some aggregates and supplementary cementing materials (SCM) combinations despite meeting the 2-year expansion criterion of the concrete prism test. This fosters a research into the effect of sample geometry and aggregate reactivity on alkali leaching and expansion of lab samples. Larger samples showed less leaching compared to standard prisms. Cylinders of 100 mm-diameter showed higher expansion than 75 mm-standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. Alkali leaching from concrete samples and alkali release from some aggregates could lead to cylindrical samples having higher expansion and better correlation to field samples compared to standard concrete prisms.

Effect of sample geometry and aggregate type on expansion due to alkali-silica reaction

Late expansions due to alkali-silica reaction were observed in field samples for some aggregates and supplementary cementing materials (SCM) combinations despite meeting the 2-year expansion criterion of the concrete prism test. This fosters a research into the effect of sample geometry and aggregate reactivity on alkali leaching and expansion of lab samples. Larger samples showed less leaching compared to standard prisms. Cylinders of 100 mm-diameter showed higher expansion than 75 mm-standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. Alkali leaching from concrete samples and alkali release from some aggregates could lead to cylindrical samples having higher expansion and better correlation to field samples compared to standard concrete prisms.

Fresh and Mechanical Properties of Self-Consolidating Concrete Incorporating Silica Fume and Metakaolin

Self-consolidating concrete (SCC) has been gaining greater interest over the past decades with its excellent offerings of efficiency, beauty, and savings. Due to its high flow ability, resistance to bleeding, and non-segregating properties, SCC holds tremendous potential for use in the construction industry. SCC requires no vibration and can fill capacities, including the ones with even the most congested reinforcements. Since SCC can be obtained by incorporating supplementary cementing materials (SCMs) such as silica fume and metakaolin. It is crucial to develop and test different SCC mixtures with different volumes of SCMs to evaluate fresh and mechanical properties. Although silica fume is used in the production of SCC, the use of metakaoline in SCC is new. In this project, eleven SCC mixtures having different volumes of silica fume and metakaolin are developed. In addition, the influence of the above mentioned pozzolans (silica fume and metakaolin) on the fresh and mechanical properties are analyzed. Recommendations on fresh and mechanical properties of silica fume and metakaoline based SCC mixtures are also provided.

Role of supplementary cementing materials on reducing damage due to internal sulphate attack in concrete

The effect of supplementary cementing materials (SCM) on internal sulphate attack in mortars was evaluated. Different types and levels of SCM were investigated where a mixture of hemihydrate and calcium carbonate fillers were used in the mixtures as a source of sulphate and carbonate, respectively. In addition, mixtures containing aggregates with high sulphate content were also examined to understand the role of sulphate from aggregate on the expansion. It has been found that the internal sulphate attack can be reduced through the use of SCM with high reactive alumina such as Metakaolin. It was hypothesised that the beneficial effect of Metakaolin lies in its ability to reduce ion mobility within the matrix, and perhaps raise the alumina/sulphur in the system favoring the formation of non-expansive monosulphoaluminate. However, at high levels of sulphate, none of the SCM provided successful protection against internal sulphate attack.

Rheological Properties Of Self-Consolidating Concrete Incorporating Natural And Industrial Pozzolans

Self-consolidation concrete (SCC) is the latest version of high performance concrete with excellent workability and high resistance to segregation and bleeding. The main objective of this project is to study the rheological properties of SCC incorporating natural and industrial pozzolans (silica fume and metakaolin, repectively) as supplementary cementing materials (SCMs). Use of such pozzolanic materials in the development of environmentally friendly and cost effective SCC can lead to sustainable construction. In this project eleven SCC mixtures are developed by incorporating different percentages of silica fume (SF) and metakaolin (MK) as replacement of cement. However, the water cement ratio of all SCC mixtures are optimized so that all mixtures satisfied the requirements of SCC in terms of fresh properties such as workability, stability, passing ability, bleeding and segregation resistance. This study particularly concentrates on evaluation of the rheological properties such as viscosity and yield stress of developed silica fume and metakaolin based SCC mixtures. The influence of SF and MK dosages on viscosity and yield stress of SCC mixtures are evaluated. Correlations among fresh and rheological properties are developed and critically reviewed to make recommendations.

Rheological Properties Of Self-Consolidating Concrete Incorporating Natural And Industrial Pozzolans

Self-consolidation concrete (SCC) is the latest version of high performance concrete with excellent workability and high resistance to segregation and bleeding. The main objective of this project is to study the rheological properties of SCC incorporating natural and industrial pozzolans (silica fume and metakaolin, repectively) as supplementary cementing materials (SCMs). Use of such pozzolanic materials in the development of environmentally friendly and cost effective SCC can lead to sustainable construction. In this project eleven SCC mixtures are developed by incorporating different percentages of silica fume (SF) and metakaolin (MK) as replacement of cement. However, the water cement ratio of all SCC mixtures are optimized so that all mixtures satisfied the requirements of SCC in terms of fresh properties such as workability, stability, passing ability, bleeding and segregation resistance. This study particularly concentrates on evaluation of the rheological properties such as viscosity and yield stress of developed silica fume and metakaolin based SCC mixtures. The influence of SF and MK dosages on viscosity and yield stress of SCC mixtures are evaluated. Correlations among fresh and rheological properties are developed and critically reviewed to make recommendations.

A study into the effects of test variables on the results of concrete tests for salt scaling and alkali-silica reaction

The ability to accurately determine in-service deterioration of concrete remains an important facet of research. This research aims to develop more reliable laboratory testing methods to better replicate in-service conditions. Two concrete deterioration modes were studied; Salt Scaling (SS) and Alkali-Silica Reaction (ASR). For SS, wrapping slabs in plastic was adopted to provide the same curing environment as curing compound for comparison to standard moist curing. Slabs with and without supplementary cementing materials were tested. The two curing methods produced different scaling results; however, results of tested samples did not change in terms of meeting or failing the acceptance limit. For ASR, modified tests focused on changing sample size to attempt to reduce alkali leaching during testing, and hence produce results that mimic long term performance of actual structures. Cube moulds were designed, manufactured, and used rather than standard prisms. Increase of specimen dimension appear to reduce leaching at 38°C.