Civil Engineering Reference
In-Depth Information
the rate of heat development accelerates during the first hours of hydration of
cement pastes containing 50% chabazite when compared with the reference
Portland cement paste. They attributed the acceleration of hydration to the
high BET surface area of the natural zeolite, rather than its fine particle
sizes.
7.5 Mixture proportions for high-volume natural
pozzolan (HVNP) concrete
HVNP concrete should be proportioned in accordance with the required
levels of workability, strength and durability, as with conventional concrete
mixtures. Due to some differences in the nature and particle characteristics
of fly ashes and natural pozzolans, typical mixture proportions show some
dissimilarity between HVFa and HVNP concrete mixtures. HVFa concrete,
in general, has 100-180 kg/m
3
Portland cement content and 150-270 kg/
m
3
fly ash content, with approximately 0.30-0.40 water to cementitious
materials (cement + fly ash) ratio (Malhotra and Ramezanianpour, 1994;
Malhotra and Mehta, 2002). The slump values of >150 mm are provided in
approximately 115 kg/m
3
water content with the help of superplasticizers in
HVFA concrete. On the other hand, Uzal et al. (2007) showed that HVNP
concrete for structural applications could be proportioned with 200 kg/m
3
Portland cement and 200 kg/m
3
natural pozzolan, with 0.45 ratio of water to
cement + pozzolan by weight w/(c + p) and slump values of 100-150 mm (Uzal
et al., 2007). Superplasticizer is a mandatory component of HVNP concrete,
and its dosage is approximately 1.5-2% by weight of total cementitious
materials content. The maximum coarse aggregate size is 19 mm in typical
examples of HVNP concrete mixtures. Typical mixture proportions for HVNP
concrete are shown in Table 7.4 (Uzal et al., 2007).
7.6 Properties of fresh and hardened high-volume
natural pozzolan (HVNP) concrete
7.6.1 Slump and workability
The incorporation of mineral admixtures generally improves the workability
of fresh concrete, which can be defined as ease of mixing, transporting,
Table 7.4
Typical mixture proportions for HVNP concrete for a slump of 100-
150 mm (Uzal et al. 2007)
Portland cement
(kg/m
3
)
Natural
pozzolan
(kg/m
3
)
Water
(kg/m
3
)
Aggregates
Superplasticizer
(kg/m
3
)
Fine
(kg/m
3
)
Coarse
(kg/m
3
)
200
200
180
820
850
2.6-6
