عمل آوری داخلی با سنگدانه های سبک وزن و تاثیر آن در خصوصیات مکانیکی بتن با سطح عملکرد بالا

HPC has become popular due to its superior mechanical and
durability properties.HPC significantly reduces maintenance
costs and enhances service life.
Internal curing of high performance concrete (HPC) by pre-saturated lightweight aggregates is a wellestablished
method of counteracting self-desiccation and autogenous shrinkage. However, by introducing the
internal water reservoirs strength and durability properties can be injured.
Concrete is a strong and durable material that has been utilized since the beginning of
civilization. It is understood that many of the early structures are deteriorating or have
already deteriorated away; however, with the knowledge of the material properties of
concrete that is available, it is hard to imagine that concrete structures is prematurely failing
before their intended service life. There are many factors involved in these failures, some of
which are due to environmental conditions and others which have arisen from human errors
or lack of knowledge.
Early age properties of concrete are vital to its long-term performance. Many
contractors and owners are interested only on the strength of concrete in 28 days or 90 days,
that they overlook the importance of other early age issue especially when the mix design has
water to cementitious material ratio (w/cm) lower than ~0.42.
Internal curing with LWA has been successfully used recently in large construction projects
of normal density concrete structures. For example, in January 2005, about 190 000 m
of
internally-cured concrete was used in a large paving project in Hutchins, Texas.
Although the benefits of internal curing for high-performance concrete structures have been
evidenced in the laboratory and some field investigations (such as those previously
mentioned), the literature does not provide any significant quantitative information regarding
the additional extension of the service life that can be achieved by the use of internal curing
in concrete structures.
A great concern for design engineers and contractors is whether the concrete will achieve the
specified compressive strength and all durability requirements in the structure during service.
Cusson & Hoogeveen (2008) demonstrated that internal curing can reduce autogenous
shrinkage considerably without affecting the strength and stiffness of high-performance
concrete. This was achieved by reducing the amount of mix water in the concrete by an
amount equal to that used in the LWA for internal curing, thus reducing the effective watercement
ratio
(w/c
) of the concrete when using higher quantities of pre-soaked LWA.
Tests by the widely accepted
methods of durability assessment, such as resistance to chloride penetration, air permeability, water
absorption, autogenous and drying shrinkage and mass loss, were conducted on HPC mixes made at water to
cement ratios in the range of 0.21–0.33. The effect of internal curing on the durability related properties of
high-performance concretes as a function of water to cement ratio is reported.