08-16-2017, 10:47 PM
internal curing concrete ppt
Internal curing offers benefits of improved hydration, reduced chloride ingress, and reduced early age cracking, which helps concrete achieve its maximum potential as a sustainable building material by extending its service life.
Internally cured concrete is not a new concept; some might even say it is ancient since it can be considered to date back to concrete constructed during the Roman Empire. What is new, however, is a more complete understanding of how internal curing (IC) works and a way to design for IC. We also have a better understanding of why IC increases the durability and service life of concrete in an economical and practical way.
What is Internal Curing?
Internal Curing is a practical way of supplying additional curing water throughout the concrete mixture. This is done by using water absorbed in expanded shale, clay or slate (ESCS) lightweight aggregate, which replaces some of the conventional aggregate in the mixture. IC is often referred to as curing concrete from the inside out.
The American Concrete Institute defines internal curing as supplying water throughout a freshly placed cementitious mixture using reservoirs, via pre-wetted lightweight aggregates, that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation
While internal curing occurs in conventional lightweight concrete, it is only recently that internal curing has been intentionally incorporated into normal weight concrete to improve its properties.
Why is Internal Curing Used?
Internal curing provides something that most concrete needs and conventional curing cannot provide: additional water that helps prevent early age shrinkage and increases hydration of cementitious materials throughout the concrete. Although IC has shown benefits at w/cm up to 0.55 (Espinoza-Hijazin and Lopez, 2010), the need for internal curing increases as the w/cm is lowered. Research shows that even in moderate w/cm (0.40 to 0.46) mixtures, the cement hydration is often not nearly complete, even after many months.
Once concrete sets, hydration creates partially-filled pores in the cement paste which causes stress that results in shrinkage. IC provides readily available additional water throughout the concrete, so hydration can continue while more of the pores in the cement paste remain saturated. This reduces shrinkage and early age curling/warping, increases strength, and lowers the permeability of the concrete, making it more resistant to chloride penetration.
Internal curing has been shown to work well with supplementary cement materials (SCM), especially at higher dosage levels, because fly ash and slag have increased water demand during their reaction, compared to hydrating portland cement. Internal curing does not replace conventional surface curing, but works with it to make concrete better. Internal curing can also help compensate for less than ideal weather conditions and poor conventional curing that is often seen in the real world.