Civil Engineering Reference
In-Depth Information
of natural pozzolans used in HVNP concrete mixtures and typical mixture
proportions of HVNP concrete. In Sections 7.4-7.6, properties of fresh and
hardened HVNP concrete are discussed, such as workability, superplasticizer
requirement, air content, setting time, strength development, modulus of
elasticity, and resistance to chloride-ion penetration. In Section 7.7, future
trends and sources of further information on high-volume pozzolan concrete
(HVPC) are presented.
7.1.1 Definition and history of development of
HVPC systems
The term high-volume pozzolan concrete dates back to the late 1980s, when
Malhotra first used high volumes of fly ash (50% by mass of total binder)
in Canada CANMET (Malhotra and Ramezanianpour, 1994; Malhotra and
Mehta, 2002). This kind of concrete was called high-volume fly ash (HVFA)
concrete, and was characterized by very low water content, and having 50%
or more of the Portland cement replaced by ASTM Class F fly ash. In order
to provide excellent workability with low water contents, superplasticizers
must be used for HVFA concrete mixtures. Comprehensive studies on HVFA
concrete have shown that it is a high-performing material, exhibiting sufficient
early-age strength, very high ultimate strength, low shrinkage and superior
durability (Malhotra and Mehta, 2002).
The use of natural pozzolans instead of fly ashes in high-volume pozzolan
cementitious systems was first proposed in a preliminary study conducted by
Uzal and Turanli (2001). HVNP systems were defined similarly to HVFA,
with 50% or more natural pozzolan by mass, and reduced water content aided
by superplasticizers. although HVNP systems initially showed relatively
poor performance in terms of strength development, further studies have
indicated that HVNP systems could perform comparably to HVFa mixtures,
if the appropriate natural pozzolanic material and superplasticizer were
selected (Uzal and Turanli, 2003, 2012; Turanli et al., 2004, 2005; Uzal et
al., 2007).
7.1.2 Significance of HVPC in the sustainable
development of concrete technology
The concrete industry is not sustainable due to its consumption of natural
resources, the huge amounts of greenhouse gases generated by Portland
cement production, and lack of durability of concrete structures. HVPC
systems provide reasonable solutions to these sustainability deficiencies.
The HVFa concrete system, which uses solid waste material from thermal
power plants, affords solutions to the all the aforementioned sustainability
issues. Fly ash is a by-product of energy production and so can be obtained
