Effect of slag coal ash and foamed glass on the mechanical properties of two-stage concrete
Two-stage concrete (TSC) is known by various names such as colcrete, Polcrete, preplaced aggregate concrete
and prepacked concrete. It is different from traditional concrete in two fundamental ways, namely
method of construction and mix proportion. Two-stage concrete (TSC) is defined as firstly, coarse aggregates
are placed into the formwork and grout is applied to fill in the between coarse aggregate particles
voids. Secondly, the percentage of coarse aggregates in the mix proportion of TSC is higher than that in
normal concrete. The typical value is about 60% as compared with 40% in traditional concrete. As coarse
aggregates are preplaced first, they can occupy up to 60–70% of the total volume. As coarse aggregates are
not involved in the mixing process, TSC is environmentally friendly with lesser consumption of energy.
With a higher content of aggregates, TSC reduces the use of cement by 20–30% and may minimize the
temperature rise. Engineering properties of TSC, including its stress–strain relationship, is mainly governed
by the properties of coarse aggregates as stress is transferred from the skeleton of aggregates to
hardened grout. Main advantages of TSC include a higher volume of coarse aggregates and the ability
to use larger size coarse aggregates. The latter also reduces the cost of crushing. TSC has beneficial properties
such as low drying shrinkage, high bonding strength, high modulus of elasticity, and excellent
durability. The method of TSC has proved particularly useful in a number of applications like underwater
construction, and masonry repair, where placement by conventional methods is extremely difficult. The
method is also applicable in case of massive concrete where low heat of hydration is required. It is studied
the feasibility of casting two stage concrete with 100% steel slag as coarse aggregate. In term of formulation,
to adopt two stage concreting method we could minimize the risk of concrete bleeding and
segregation due to high water absorption and quite high density of slag aggregate. The effect of slag coal
ash and foamed glass on the mechanical properties of two-stage concrete has rarely been reported. Thus,
the development of an eco-efficient alkali-activated grout for two-stage concrete is a new research topic
that has no robust results to draw solid conclusions and it should blaze the track towards a cleaner production
of building materials with outstanding sustainability.
Hakim S. Abdelgader(1-2022)
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