Search results
Results from the WOW.Com Content Network
The curing of concrete when it continues to harden after its initial setting and progressively develops its mechanical strength is a critical phase to avoid unwanted cracks in concrete. Depending on the temperature (summer or winter conditions) and thus on the cement hydration kinetics controlling the setting and hardening rate of concrete ...
When water is added to cement, each of the compounds undergoes hydration and contributes to the final state of the concrete. [2] Only calcium silicates contribute to the strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). [3] Dicalcium silicate, which reacts more slowly, only contributes to late strength.
A fairly well-defined reaction front can often be observed in thin sections; ahead of the front the concrete is normal, or near normal. Behind the reaction front, the composition and the microstructure of concrete are modified. These changes may vary in type or severity but commonly include: Extensive cracking; Expansion
To attempt to simplify and to stylize a very complex set of various reactions, the whole ASR reaction, after its complete evolution (ageing process) in the presence of sufficient Ca 2+ cations available in solution, could be compared to the pozzolanic reaction which would be catalysed by the undesirable presence of excessive concentrations of alkali hydroxides (NaOH and KOH) in the concrete.
Alkali–aggregate reaction is a term mainly referring to a reaction which occurs over time in concrete between the highly alkaline cement paste and non-crystalline silicon dioxide, which is found in many common aggregates. This reaction can cause the expansion of the altered aggregate, leading to spalling and loss of strength of concrete.
The alkali–carbonate reaction is an alteration process first suspected in the 1950s in Canada for the degradation of concrete containing dolomite aggregates. [1] [2]Alkali from the cement might react with the dolomite crystals present in the aggregate inducing the production of brucite, (MgOH) 2, and calcite (CaCO 3).
A retarder is a chemical agent that slows down a chemical reaction. For example, retarders are used to slow the chemical reaction hardening of plastic materials such as wallboard, concrete, and adhesives. [1] Sugar water acts as a retarder for the curing of concrete.
Samples of "ground granulated blast furnace slag" (left) and "granulated blast furnace slag" (right) Ground granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.