Thin layer of dust on coarse and fine aggregates is responsible for reduction in bond stress in concrete. Dust may also interfere chemical reaction between cement and water. Polluted water will affect hydration process and may responsible for corrosion of steel. Clean aggregates should be used. But may no available every time and every where.
Dusty aggregates will prevent effective bonding of the cement paste with the aggregate thereby creating a weaker interfacial transition zone that can consequentially affect the strength and durability properties of the concrete. Also, the dusts can absorb the water meant for hydration thereby leaving the concrete with several unhydrated areas which will lead to lower strength of the concrete and correspondingly lower resistance to some chemical and physical attacks
Deleterious compounds present in polluted water water can alter the hydration process thereby leading to incomplete hydration or formation of compounds that are detrimental to the integrity of the concrete. In addition, if the substance that pollute the water are highly alkali, they can kick start alkali aggregate reaction in concrete with certain types of reactive silica.
The dusty aggregates are very band to be used as cement aggregate due to their effect in forming strong bond. We usually wash aggregates before mixing to remove dust and other impurities.Similarily, polluted water may dgrede the strength of the resultant concrete then by reducing its durability.
The presence of dust over the surface of aggregates leads to the development of a weak bond between the aggregates and cement paste, which further affects the interfacial transition zone, and creates a weak and less durable concrete matrix. Additionally, the mix proportions framed for the concrete mix will have to be adjusted to ensure the desired workability, and establish proper hydration between cement and water.
The use of polluted water in concrete can interfere with the hydration process, and lead to the formation of a weak concrete material.
The dust on the top of coarse aggregates affects the strength of the concrete due to it negative impact on the mico-structure of concrete. The polluted water could affect durability and strength depending on the containment
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