Alkali Aggregate Reaction in Concrete

radical Aggregate Re legal action in ConcreteConcrete is matchless of the most construction material composed of water, coarse and fine aggregative and cementum (binder)which fills the space between essence and stick them together. Concrete exertion is m-sensitive. Concrete become stronger and capable of bearing loads with the initiation of solidifying process. There atomic number 18 two types of cover, create mixing plants and central mix plants. A ready mix plant is the mix of entirely ingredients debar water, while a central mix plant is the mix of all ingredients with water this method needs more quality control than ready mix (Neville, 1996).After mixing all ingredient and place it, bent the cover is absolutely essential to achieve best strength and hardness. For achieving the strength, cement needs a moist and controlled environment.Good concrete elements are the elements which has a good durability. intensity level is defined as the ability of concrete to endu re chemical attack, abrasion and during its life time. If the concrete elements have factors below, they go away last out durableThe cement paste has low permeabilityIts better to do with well graded hoard up.The ingredient should have minimum impurities such as Sulphates, Chlorides, radical and etc.So in the absence of one or more of these factors, the concrete will face with the durability problem. deuce major types of durability problem are (ACI 201.2R-08, 2008)Durability against physical actionDurability against Chemical actionPhysical durability consists ofTemperature stressesFreezing and thawing actionAnd chemical durability consists of (Neville, 1996)Sulfate attackChloride ingressCorrosionAlkali Aggregate response2.2 Alkali Aggregate Reaction2.2.1 Backgrounddoubting Thomas Stanton (Munn et. al., 2011) at California Department of Transportation detected cracking in concrete which was occurred due to certain aggregate reacting with cement alkalis for the first time there fore he called this phenomena Alkali-aggregate reception (AAR). Since then, several scientists continue researching on AAR, with the main(prenominal) areas of focus as (Fournier Berube, 2000)Better understanding of mechanism of AAR in concrete. naming of reactive aggregate and developing test methods to assess the reactivity of aggregates. develop new method to pr unconstipatedt initiation of AAR in new structures underdeveloped remedies for rehabilitation of existing structures affected by AAR.2.2.2 Alkali Aggregate Reaction (AAR)When a highly basic fluid which consist of alkali hydroxides ions homogeneous (K+, Na+ OH) fill the pores in concrete and the aggregate in concrete are chemically unstable in the high pH environment, the concrete encounter with distresses such as cracking, losing serviceability, and etc. (Fournier Berube, 2000). This internal chemical reaction is recognized as alkali aggregate-reaction (AAR). The source of alkalinity in these phenomena is from cemen t and aggregate but some external sodium or potassium sens contribute the reaction (Munn et. al., 2011). The reaction cause the formation of a change which absorbs water and then expands, due to this internal pressure, the micro cracks gradually appear. (ACI 221.1R-98, 1998) ii types of AAR are generally recognized 1) Alkali- carbonate reaction (ACR) and 2) Alkali silicon oxide reaction (ASR) .2.2.2.1 Alkali-Carbonate Reaction (ACR)Argillaceous dolomitic limestones are susceptible to this reaction. Two mechanisms contribute to the carbonate reaction 1) Crystallization of brucite and calcite during the dedolomitision and 2) Sorption of alkalis by clay.The dedolomitision causes expansionCaMg(CO3)2 + 2 (Na,K)OH Mg( OH )2 + CaCO3 + ( Na,K )2CO3DolomiteThis reaction is known to not to occur frequently to this phenomenon are less common and suitable for exploitation in concrete exertion (Fournier Berube, 2000). The aggregate sensitive to ACR have characteristics texture which ord ure identify by some tests such as ASTM C 441 or ASTM C586-11.The dedolomitisation involves the reaction of alkali carbonates with portlandite in concrete and yield to reform alkali hydroxides (Fournier Berube, 2000).(Na,K)2CO3 + Ca (OH ) 2 CaCO3 + 2 ( Na, K) OHNo gel is produced as a result of this reaction. deep the theory which was introducing by Katyama (Katyama, 2010) in the early of 20th century suggests that ACR is the combine reaction of dedolomitisation of dolomitic aggregate and high-flown ASR of cryptocrystalline was confirmed by using tests like SEM observation, polished section and etc. (Katayama, 2010)2.2.2.2 Alkali-Silica Reaction (ASR)Alkali-silica reaction is relatively more common and it has negative effect on the mechanical properties of concrete (Marzouk Langdon, 2000) this reaction is between alkaline pore solution and silica mineral like cryptocrystalline quartz and opal. Higher solubility of silica mineral in high pH solutions means higher likelihood of reaction occurrence. The reaction yields the formation a gel that absorbs water and expands in moist areas (Munn et. al., 2011). The expansive pressure by the silica gel causes crackings and deteriorations in concrete. The quantity of gel depends on the amount of silica if the amount of silica increases, the expansion will be increased.The composition of this gel has been studied by several of researchers (Lindgard et al., 2012) they give tongue to that, this gel has high contents of silica and low contents of atomic number 20 and alkalis. The formation of silica gel depends on composition and the texture of the aggregate but the composition of silica gel doesnt depend on the record of aggregate.Two categories of ASR are recognizedQuartz- bearing rock which reacts slowly in the early ages and then the expansion and cracks start to appear from 10 to even 25 years of concrete, when concrete is exposed to conditions favoring the reactionsThe rocks incorporate with Silica. This type of rocks contributes to extended expansion and cracking on the early age of concrete when concrete is exposed to conditions favoring the reactionsASR damages both macroscopical and microscopic properties of material, for instance for macroscopic damages, the changes in length can be mentioned, as Hayman et.al.(Hayman et al., 2010) stated that evil of concrete is when the expansion greater than 0.040%. For microscopic damages, significant difference between modules of elasticity of the gel and cement paste or aggregate can be mentioned (Chen et al., 2010).