Durability of concretes containing ground granulated blast furnace GGBS against sulfate attack

Ground granulated blast furnace GGBS (GGBS), a by-product of the steel manufacturing industry, being used as an effective partial cement replacement material, has already been proven to improve several performance characteristics of concrete. The reactivity of GGBS has been found to depend on the properties of GGBS, which varies with the source of GGBS, type of raw material used, method and the rate of cooling. In this paper cement replacement levels of 35%, 42.5% and 50% were selected to study the effects of GGBS on compressive strength and sulfate resistance in concretes. Two tests were used to determine the resistance of GGBS concrete to sulfate attack. These tests involved immersion in 5% sodium sulfate solutions. Furthermore, compressive strength of concrete mixtures that keep in water and sodium sulfate were determined at ages up to 180 and 270 days respectively. Also mass change of concrete mixtures were determined. The experimental results show that at later ages GGBS concrete that keeps in water got closer compressive strength to control concrete. After 270 days of exposure to the sodium sulfate solutions, in mixtures containing 50% GGBS replacement by Portland cement had rather growth compare to 35% GGBS replacement by Ordinary Portland Cement (OPC). Key word. Ground granulated blast furnace GGBS, mechanical properties, durability, sulfate attack INTRODUCTION It is a well-known fact that the causes of damage in concrete are freezing, water penetration, chemical degradation and erosion. Therefore, it is important that durability of concrete be enhanced. This can be accomplished by some additives which improve the properties of both freshly mixed concrete and hardened concrete by pozzolanic reaction. Benefits of using additional binder materials on the durability of concrete are well established. Highperformance concrete may contain materials such as fly ash, silica fume, ground granulated GGBS, natural pozzolana , fibers, chemical admixtures and other materials, individually or in various combinations. These materials can enhance the strength and durability of concrete, simultaneously, rendering them recommendable for use in concrete industry. Also It is an efficient procedure for the cement industry in order to decrease CO2 emissions, which represents about 5% of the total anthropic emissions in the world (Brand 2004). In addition, it can contribute to save natural resources, recycle by-products and preserve the environment. Ground granulate blast furnace GGBS (GGBS) is a by-product from the iron industry; it is one of the most commonly used additions in the cement industry. According to the manufacturing process, GGBS is a quite variable material due to the variability of its chemical composition. Offering latent hydraulic properties when mixed with clinker cement, hydration of GGBS is directly related to its hydraulicity: the dissolution of GGBS glass fraction is ensured by hydroxyl ions (OH ) resulting from the hydrolysis of Portlandite Ca(OH)2 produced by the hydration of clinker (Glasser 1996, Regourd 1995). The hydration products formed in the cement matrix are mainly additional hydrated calcium silicates and aluminates (CSH, CAH). The resulting hydrated cementitious matrix presents good chemical resistance and a more refined pores structure (Ye 2009, Cheng 2005). Therefore the mechanical performance and durability of concrete are improved. Many studies show that, in sufficient quantities, GGBS is generally very effective in controlling sulfate attack. GGBS is a latent hydraulic material and is very successful in lowering permeability of concrete. It also improves sulfate resistance by diluting Ca(OH)2. ACI201.2 recommends the use between 40 and 70% GGBS by mass replacement to achieve satisfactory sulfate resistance. Based on a long term study by Building Research Establishment in the UK. on the effects of GGBS on concrete durability, minimum of 70% GGBS (by mass) is recommended in combination with GU cement in severe sulfate exposures (Osborne 1999). results were observed by Brown, Hooton and Clark (2004), who showed that low alumina GGBS was effective in increasing resistance to magnesium and sodium sulfate attack at 45% and 72% replacement level when used with Type I cement. EXPERIMENTAL PROGRAM Description of materials Locally available type I ordinary Portland cement (OPC) complying with Iranian specification 389, with a fineness of 2800 cm 2 / g was used for mortar and concrete mixes. The GGBS used in this research project was produced in the iron steel company of Zobahan Esfahan (Iran). The GGBS was ground in a laboratory mill to a Blaine fineness of 4200 cm 2 /g. The physical properties and chemical composition of cement and GGBS are given in Table 1 and Table 3, respectively. Also the physical properties of coarse aggregate and fine aggregate are given in Table 2. Table 1. Physical properties of OPC and GGBS Property OPC GGBS Specific gravity 3.15 2.85 Specific surface (cm 2 /g) 2800 4200 Ignition loss (%) 0.91 Color Gray whitish (off-white) Table 2. Physical properties of coarse aggregate and fine aggregate Aggregates type Specific gravity W b (%) D max Coarse aggregate 2.57 1.6 12.5 Fine aggregate 2.56 2.6 D max: maximum aggregate size Table 3. Chemical compositions of OPC cement and GGBS Compound (%) OPC GGBS SO3 2.570 2.49 K2O 0.63 0.90 Na2O 0.36 0.38 CaO 65.34 65.34 SiO2 20.83 37.50 MgO 2.17 8.60 Al2O3 4/34 6.40