Jay G. Sanjayan

Alkali activation of Australian slag cements

Abstract Investigation of alkali activation of Australian slag (AAS) was carried out using sodium silicate, sodium hydroxide, sodium carbonate, sodium phosphate, and combinations of these activators. Compressive strengths in the range from 20 to 40 MPa were achieved for the pastes. The most effective activator was liquid sodium silicate. With this activator, the effect of curing at 60 °C, modulus (M s ) of sodium silicate solution and concentration of alkalis on the compressive strength and setting times have been studied. On the basis of this investigation, a sodium silicate solution with a low Na content and M s = 0.75 is recommended for formulation of AAS concrete.

Resistance of alkali-activated slag concrete to acid attack

This paper presents an investigation into the durability of alkali-activated slag (AAS) concrete exposed to acid attack. To study resistance of AAS concrete in acid environments, AAS concrete was immersed in an acetic acid solution of pH=4. The main parameters studied were the evolution of compressive strength, products of degradation, and microstructural changes. It was found that AAS concrete of Grade 40 had a high resistance in acid environment, superior to the durability of OPC concrete of similar grade.

Effect of pore size distribution on drying shrinkage of alkali-activated slag concrete

Higher drying shrinkage has been observed in alkali-activated slag concrete (AASC) than comparable ordinary Portland cement concrete (OPCC). However, the OPCC samples lost more moisture during the period of shrinkage measurements than the AASC samples. This is contradictory to the commonly accepted relationship between shrinkage and moisture loss. This paper provides an explanation for this phenomenon by studying the effect of pore size distribution on the drying shrinkage. The investigation showed that AAS pastes have a much higher proportion of pore sizes within the mesopore region than OPC pastes. Further, the radius of pores where the meniscus forms seems to be an important parameter in determining the magnitude of shrinkage, rather than the amount of moisture loss. This also supports the theory that the capillary tensile forces set up during drying is an important contributory factor for the drying shrinkage of concrete.

Workability and mechanical properties of alkali activated slag concrete

This paper reports the results of an investigation on concrete containing alkali activated slag (AAS) as the binder, with emphasis on achievement of reasonable workability and equivalent one-day strength to portland cement concrete at normal curing temperatures. Two types of activators were used: sodium hydroxide in combination with sodium carbonate and sodium silicate in combination with hydrated lime. The fresh concrete properties reported include slump and slump loss, air content, and bleed. Mechanical properties of AAS concrete, including compressive strength, elastic modulus, flexural strength, drying shrinkage, and creep are contrasted with those of portland cement concrete.

Sulfate attack on alkali-activated slag concrete

Abstract This paper presents an investigation into durability of alkali-activated slag (AAS) concrete in sulfate environment. Two tests were used to determine resistance of AAS concrete to sulfate attack. These tests involved immersion in 5% magnesium sulfate and 5% sodium sulfate solutions. The main parameters studied were evolution of compressive strength, products of degradation, and microstructural changes. After 12 months of exposure to the sodium sulfate solution, the strength decrease was up to 17% for AAS concrete and up to 25% for ordinary Portland cement (OPC) concrete. After the same period of exposure to the magnesium sulfate solution, the compressive strength decrease was more substantial, up to 37% for OPC and 23% for AAS. The main products of degradation were ettringite and gypsum in the case of Portland cement and gypsum in AAS. OPC samples had significant expansion, cracking, and loss of concrete, while AAS samples were not expanded but cracked in the test. During experiments with the sodium sulfate solution, some increase in strength of AAS concrete was recorded, likely due to continuing hydration.

Effect of admixtures on properties of alkali-activated slag concrete

This paper reports the results of an investigation on concrete that incorporated alkali-activated slag (AAS) as the only binder. The activators were liquid sodium silicates (4–7% Na, mass of slag) and a multi-compound activator (NaOH+Na2CO3) (8% Na, mass of slag). AAS utilizes industrial by-products and develops high early strength. However, some of its properties such as high shrinkage and poor workability impede its practical application. Admixtures used for ordinary portland cement (OPC) were tested to improve these properties of AAS concrete. Superplasticiser based on modified naphthalene formaldehyde polymers (S), air-entraining agent (AEA), water-reducing (WRRe), shrinkage-reducing (SHR) admixtures at dosages of 6–10 ml/kg, and gypsum (G) (6% of slag weight) were used. The paper presents the study of workability in the fresh state, shrinkage and compressive strength of AAS concrete, and the effect of admixtures and type of activator on these properties. Concrete activated by liquid sodium silicate had the best mechanical properties. AEA, SHR, and G significantly reduced its shrinkage. AEA also improved workability and had no negative effect on compressive strength. On the basis of this investigation, AEA was recommended for use in AAS concrete.

Effect of elevated temperature curing on properties of alkali-activated slag concrete

This investigation is focused on the effect of curing temperature on microstructure, shrinkage, and compressive strength of alkali-activated slag (AAS) concrete. Concrete prepared using sodium silicate and sodium hydroxide as the activator had greater early and flexural strength than ordinary Portland cement concrete of the same water/binder ratio, but it also had high autogenous and drying shrinkage. Heat treatment was found to be very effective in reducing drying shrinkage of AAS concrete and promoting high early strength. However, strength of AAS concrete at later ages was reduced. Microstructural study revealed an inhomogeneity in distribution of hydration product in AAS concrete that can be a cause of strength reduction. Pretreatment at room temperature before elevated temperature curing further improved early strength and considerably decreased shrinkage in AAS concrete.

MICROCRACKING AND STRENGTH DEVELOPMENT OF ALKALI ACTIVATED SLAG CONCRETE

Abstract Alkali activated slag concrete (AASC) is made by activating ground granulated blast furnace slag with alkalis without the use of any Portland cement. This study investigates the level of microcracking which occurs in AASC when subjected to various types of curing regimes. The corresponding compressive strength developments of AASC were monitored. The level of microcracking were measured using three different types of tests: (1) frequency and size of surface cracks using crack-detection microscope (2) water sorptivity tests measuring absorption of water by capillary attraction and (3) mercury intrusion porosimetry (MIP) tests which measured the pore size distribution of AASC and AAS pastes (AASPs). The results show that the lack of moist curing of AASC increased the level of microcracking measured using all three different tests mentioned above. The strength development of AASC is also significantly reduced by lack of moist curing.

Resistance of alkali-activated slag concrete to carbonation

Abstract This paper presents an investigation into durability of alkali-activated slag (AAS) concrete exposed to carbonation. Two tests were used which simulated exposure of AAS concrete to carbonated solution and to atmosphere high in carbon dioxide. These tests involved immersion of the concrete in 0.352 M sodium bicarbonate solution, and exposure to atmosphere with 10–20% of CO 2 at 70% relative humidity. It was found that the resistance of AAS concrete to carbonation was lower than that of ordinary Portland cement (OPC) concrete, and AAS concrete had higher strength loss and depth of carbonation than OPC concrete in both tests.

Cracking tendency of alkali-activated slag concrete subjected to restrained shrinkage

Alkali-activated slag concrete (AASC) has higher drying shrinkage than ordinary Portland cement concrete (OPCC). However, the cracking tendency of AASC under drying conditions, when restrained, is unreported. AASC has lower elastic modulus, higher creep, and higher tensile strength than OPCC, and the combined effects of these can affect the cracking tendency of AASC. This article reports the results of cracking tendency utilizing restrained ring tests and discusses the development of a restrained beam test. The effects of curing, aggregate type, and incorporation of shrinkage reducing chemical admixture on the cracking tendency of AASC are reported.