Civil, Environmental and Chemical Engineering

This paper presents a study to assess the effects of site exposure on the durability of concrete cast with ordinary Portland cement (OPC), pulverised fl y ash (PFA) and ground granulated blast furnace slag (GGBS) using the controlled permeability formwork (CPF). An experimental program has been undertaken in which trial specimens have been placed on exposure sites at coastal locations in Australia. Various non-destructive tests were conducted such as Schmidt hammer, water permeability, air permeability, ultrasonic pulse velocity, steel potential mapping, linear polarisation resistance corrosion rate monitoring, chloride diffusion, accelerated chloride diffusion, and resistivity. The durability data are presented to compare the effects of using CPF with those of traditional (plywood) formwork for OPC, PFA and GGBS concrete mixes, as specifi ed on actual construction projects in Australia. The results indicate that CPF gave improved performance compared to the traditional formwork for surface properties of concrete.

The environmental impact from the production of cement has prompted research into the development of concretes using 100 % replacement materials activated by alkali solutions. This paper reports the assessment of a number of key durability parameters for geopolymer concrete made from fly ash activated with sodium silicate and sodium hydroxide. Properties investigated have included workability, compressive strength, water sorptivity, carbonation, chloride diffusion and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that both the geopolymer concretes with activator modulus 1.00 and 1.25 gave durability parameters comparable to Ordinary Portland and blended cement concretes of similar strength, while the geopolymer concrete with an activator modulus of 0.75 displayed lower durability performance. However, there is a concern over the long term performance of the geopolymer concretes with activator modulus of 1.00 and 1.25 when considering chloride induced corrosion of reinforcing steel due to the initial pH and long term chloride diffusion coefficient.

This paper presents the effect of nano silica, used individually and in combination with set accelerator or hydrated lime, on the properties of high volume fly ash (HVFA) cement composites, replacing 70 % of cement. Compressive strength test along with X-ray diffraction and thermogravimetric analysis were undertaken to study the effect of various elements on the physico-chemical behaviour and the pozzolanic activity of the blended samples. The addition of 5 % nano silica improved the 7 day strength of the blended sample by 76 % and by further increasing the nano silica content to 7.5 %, the 7 day strength increased by 94 %. However, at 28 days both 5 and 7.5 % nano silica modified samples showed approximately the similar improvement in strength i.e. 54 and 50 % respectively. With the addition of set accelerator to nano silica modified HVFA cement blend, there was a considerable reduction in both 7 and 28 day strengths. Addition of 5 % hydrated lime to HVFA blend, modified with 5 % nano silica showed no effect on the further improvement of strength. However, when 5 % hydrated lime was added to the 7.5 % nano silica modified HVFA blend, there was a considerable reduction in both 7 and 28 day strengths. This demonstrates that nano silica is highly effective in improving the strength of high volume fly ash cement blends when used alone, but when it is used in combination with either hydrated lime or set accelerator, shows no or negative effect on the development of strength.

This paper presents a quantitative study of the effect of 5 and 7.5% of nano silica (nS), 2.5 and 5% of nanoalumina (nA) and 2.5 and 5% of nanocalcium carbonate (nCC), on the properties of very high-volume fly ash cement composites (VHVFA-CC), replacing 80% of cement. Compressive strength test, thermogravimetry, quantitative X-ray diffraction and scanning electron microscopy were undertaken to study the effect of various nanomaterials on the physicochemical behaviour of VHVFA cement composites. The results show that the addition of nS to VHVFA-CC significantly improves its compressive strength and considerably increases the formation and thermal stability of silica-rich hydrogarnet [Ca3(AlxFe1−x)2(SiO4)y(OH)4(3−y)], which increases with the increase in nS content. The addition of nCC to VHVFA-CC does not show any effect on the pozzolanic reaction at 7 days of curing but at 28 days considerably improves its pozzolanic reaction, which increases with the increase in nCC content. The addition of nA though improves the hydration/pozzolanic reaction of VHVFA-CC, resulting in the improvement of compressive strength, but only if added in small quantities (i.e. 2.5% or less). If it is added in higher amounts, it promotes the formation of Al(OH)3 gel that severely inhibits the hydration/pozzolanic reaction within the cement matrix.