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directly on the gravel while the second one is placed above ground, on two 200 mm in diameter by 0.40 m long concrete cylinders cut lengthwise (Fournier & Malhotra 1996). The concrete slabs are placed directly on the compacted gravel pad, with granular material being placed around and between each of them so that only the top surface of the
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Alkali-silica reaction (ASR) is one of the major degradation causes of concrete. This highly deleterious reaction has aroused the attention of researchers, in order to develop methodologies for its …
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The content of alkali in cement can be calculated as Na 2 O + 0.658K 2 O as a selective index. Alkali content in cement should not exceed 0. 60% or be determined by consultation if active aggregate is used. ... The alkali activity of gravel or pebbles in concrete should be tested for concrete exposed to moisture for a long time. When …
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1. Introduction. One of the keynote papers dedicated to the 13th International Congress on the Chemistry of Cement held in Madrid in 2011 focused on the chemistry of alkali-activated binder systems [1].The aim of the current paper is not to provide a detailed overview of all aspects of the history, chemistry and engineering of alkali-activated …
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Alkali Silica Activity and Inhibition Measures of Concrete Aggregate in Northwest China Jing Wen 1,2, Jinmei Dong 1,2, *, Chenggong Chang 1,2, Xueying Xiao 1,2 and Weixin Zheng 1,2, *
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1. Introduction. Alkali–silica reaction (ASR) is one of the most frequent causes of concrete deterioration [1,2].ASR is a slowly expansive reaction between certain forms of alkali-reactive silica (opaline silica, flint, cryptocrystalline quartz) and/or certain silicate minerals present in concrete aggregates and the hydroxyl ions in concrete pore …
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occurs when the water soluble alkali content of the cement was abQut 0.6% Na20 equivalent which corresponds to an acid soluble alkali CQntent of about 0.8%. By contrast, with slowly expanding aggregates such as greywackes and hornfels expansion increases with the alkali content of the cement, at least up to an acid soluble alkali …
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By using of accelerated mortar bar test (AMBT), concrete prism method (CPM), and rock column method (RCM), it confirms that aggregates of W1# are the aggregates with potential alkali-silica activity. It is advisable to use a variety of methods to evaluate whether the aggregates have the potential activity.
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The huge demand for sand and gravel resources in road engineering construction leads to excessive consumption of resources and environmental damage. Recycling waste concrete and industrial solid waste as a road material is a promising alternative. In order to explore the application of these solid wastes in the road base, this …
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For the alkali-activation of high-calcium precursors, calcium (Ca +) has shown that it can act as a charge balancing cation like Na + and K +.If some of the Na + is replaced by Ca +, a C-A-S-H gel is formed (calcium aluminosilicate hydrate).Recent studies, show that the higher pH of the medium, the more C-A-S-H will prevail over N-A-S-H [24, …
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In addition, the alkali content from cement pose a stronger effect on the AAR expansion of RCA. By studying the AAR of recycled concrete incorporating 30% replacement of RCA when using low and high alkali cement respectively. The RCA concrete using high alkali cement expanded more than twice that of using low alkali …
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The use of concrete is associated with immense negative environmental impacts. The current annual production of>4 billion tonnes of ordinary Portland cement (OPC) is responsible for 7% of the global CO 2 emissions [3]. Concrete has an environmental impact of 300 kg eq CO 2 /m 3 on average, of which 90% is attributable …
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Conventional porous concrete is fabricated with gravel and cement, showing low P removal efficiency due to low porosity, inferior surface area, and low active components of gravel. Accordingly, a novel porous concrete (C-A) is synthesized by replacing gravel with alkali-activated aggregate (compressive strength of 90.12 MPa …
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Slag (SiO 2 +CaO>70%) is the most commonly used calcium-rich precursor for forming the high calcium alkaline cement, and the main reaction product is an aluminum-substituted calcium silicate hydrate (C-A-S-H gel) which is similar to the product generated during Portland cement hydration (C-S-H), but its Ca/Si ratio is lower than …
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ASTM C1778, Standard Guide for Reducing the Risk of Deleterious Alkali-Aggregate Reaction in Concrete and AASHTO R 80, Determining the Reactivity of Concrete Aggregates and Selecting Appropriate Measures …
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The test procedure involves using high-alkali cement, meeting an alkali content of 0.90 % ± 0.10 % and adding sodium hydroxide to the mix water to raise the cement alkalis to 1.25 %. Concrete prism (from such mix) measuring 75 mm x 75 mm x 285 mm (3-in x 3-in x 11.25-in ) is cured in water for one full year at 38 °C (100 °F).
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SEM examination was used during the concrete alkali active long-term aging tests to understand qualitatively the alkali activity reaction degree and to predict the deterioration trend of the concrete. The Alkali-silica Reaction (ASR) is one of the most important factors affecting the durability of concrete [1].
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of alkali-activated cementitious materials [4], but there is limited research on the double damage of chloride ion corrosion and freeze-thaw damage of alkali-activated coal gangue cementitious materials. Calcined coal gangue has better activity when it reaches 700 C [5,6], and then the alkali-activated coal gangue-slag can be employed as a cement.
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2. Background. AAMs are synthesized by the reaction of an aluminosilicate-based precursor (xSiO 2 ∙ yAl 2 O 3), alkali activators (MOH and M 2 SiO 3; where M is either alkali ion Na + or K +) and water (H 2 O). No Portland cement is required to produce alkali-activated binders, but AAMs could also be added as a supplementary …
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The feasibility of composite-activated coal gangue (CACG) as the primary cementitious material for concrete was experimentally studied in this paper. The effects of concrete strength grade on slump and slump flow, compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and drying shrinkage of alkali …
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Research on alkali-activated cement has investigated the possibility of using recycled concrete for alkali activation (Borrachero, 2022; Viswanath, 2021), crack development (Matalkah, 2019), and ...
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The ordinary Portland cement (P.O 42.5) with a specific surface area of 345 m 2 /kg and a density of 3.15 g/cm 3 was used, which was provided by Shijiazhuang Quzhai cement co. LTD. Slag and fly ash were produced in Lingshou, Shijiazhuang. The slag with a specific surface area 455 m 2 /kg and a density of 2.82 g/cm 3 was classified as S105 …
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During the last several decades, Alkali-activated Materials (AAMs) is a Portland cement-free form, have been intensively researched as a potential alternative for ordinary Portland cement concrete (OPCC), with the objective of lowering CO2 emissions while repurposing a large volume of industrial waste by-products.
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The alkali−silica reaction (ASR) is a chemical reaction that occurs between hydroxyl ions in the pore solution of a hydrated cement paste and in certain reactive silica phases in the aggregates used in …
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The now well-known alkali-activated cement (AAC), which has a lower carbon footprint, and excellent durability in some applications, ... The alkali activities of the ES and EP were evaluated using the ASTM C1260 standard (Standard Test Method for Potential Alkali Reactivity of Aggregates). The accelerated mortar bar test assessed by the length ...
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e been developed for assessing the potential alkali-reactivity of aggregates. These …
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a Concrete pore solution is dominated by Na, K, and OH (with minor amounts of Ca). If the silica in the aggregate is reactive — the OH and then the Na and K will react with the SiO 2.. b The product of the reaction is in alkali-silica gel composed of Na, K, Ca, and Si The gel forms around and within the aggregate.c The gel imbibes …
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2.3. Test methods. To evaluate the potential reactivity of the gravel aggregate, the accelerated ASTM C1260 method was used together with the long-term ASTM C227 method [18], [19].The grain composition was prepared from the mechanically crushed gravel aggregate according to the requirements outlined in ASTM C1260 and …
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Quality Counts. Make sure that your concrete producer purchases good-quality aggregate as verified by regular aggregate test results in compliance with ASTM C 33, "Standard Specifications for Concrete Aggregates." A history of good performance of a local aggregate also provides an indication of how well the material performs in service.
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This test method is generally considered the most reliable for evaluating aggregate …
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