The quality of pure Slag is according to the ASTM Standard C-989. We have supplied Pure Slag on mega projects to
M/s CWE at Mangla Dam Raising Project. M/s Sambu Construction Co. (Korean) at 84-MW New Bong Escape Hydro Electric Project, Lehri Mirpur (AJK) & Golen Gol Hydro project Chitral. M/s Descon Engineering Pvt Ltd. at Jinnah Barrage, Mianwali. & Wind Power Project, Gharo. M/s CGGC at Neelum
Jhelum Hydro Power Project, Muzafrabad
Brief Description of GGBF Slag
1. Ground Granulated Blast Furnace Slag
Ground Granulated Blast Furnace Slag (GGBFS) is a by-product of the steel industry. Blast furnace slag is defined as “the non-metallic product consisting essentially of calcium silicates and other bases that is developed in a molten condition simultaneously with iron in a blast furnace.” [1] In the production of iron, blast furnaces are loaded with iron ore, fluxing agents, and coke. When the iron ore, which is made up of iron oxides, silica, and alumina, comes together with the fluxing agents, molten slag and iron are produced. The molten slag then goes through a particular process depending on what type of slag it will become. Air-cooled slag has a rough finish and larger surface area when compared to aggregates of that volume which allows it to bind well with portland cements as well as asphalt mixtures. GGBFS is produced when molten slag is quenched rapidly using water jets, which produces a granular glassy aggregate.
2. Classification
In accordance with ASTM C989, GGBFS has three strength grades which are determined by their respective mortar strength when they are mixed with equal mass of portland cement. The three grades, 80, 100, and 120, are classified according to their slag activity index which is average compressive strength of the slag-reference cement cubes (SP), divided by the average compressive strength of the reference cement cubes (P), multiplied by 100.
3. Chemistry
Slag is primarily made up of silica, alumina, calcium oxide, and magnesia (95%). Other elements like manganese, iron, sulfur, and trace amounts of other elements make up about other 5% of slag. The exact concentrations of elements vary slightly depending on where and how the slag is produced. When cement reacts with water, it hydrates and produces calcium silicate hydrate (CSH), the main component to the cements strength, and calcium hydroxide (Ca(OH)2). When GGBFS is added to the mixture, it also reacts with water and produces CSH from its available supply of calcium oxide and silica. A pozzolanic reaction also takes place which uses the excess SiO2 from the slag source, Ca(OH)2 produced by the hydration of the Portland cement, and water to produces more of the desirable CSH making slag a beneficial mineral admixture to the durability of concrete.
4. GGBFS Effects on Flexural and Compressive Strength
GGBFS has a positive effect on both the flexural and compressive strength of concrete after 28 days. In the first 7 days the compressive strength is generally slightly lower than pure 100% Portland cement mixtures. In the 7 to 14 day range, the compressive strength is about
equal to the strength of concrete without slag. The real gain in strength is noticed after the 28 day mark especially when 120 grade GGBFS is used. [2]. A 1992 study which showed that the flexural strength of concrete mixes with different slag replacement percentages was between 6.0-6.8 MPa at 14 days [3]. The long term strength of slag cement depends on many factors such as the amount of slag and Portland cement, and water to cement ratio.
5. Slag cement in Self Consolidating Concrete (SCC)
The use of slag as a replacement of cement in SCC mixtures was shown to be effective in a 2003 study. The slag cement content was varied in different SCC mixtures. The SCC mixtures with the slag cement had slump flow and flow times similar to the control mixtures. The compressive strengths for the mixtures with the slag cement met their target strengths by 28 days, reaching 31-46 MPa compressive strength. Cost was also a consideration for this study and the most cost effective mixture had a 60% slag replacement. [4]
6. Shrinkage
One report states that the shrinkage of GGBFS is similar to the shrinkage of plain concrete and thus does not require any special engineering or construction requirements [2]. A study in 2003 showed that plain concrete and concrete with silica fume developed drying shrinkage faster than concrete with GGBFS, but that after one year the shrinkage was about the same for all the types of concrete that were tested. With respect to autogenous shrinkage, the study showed that the higher the percentage of slag used, the higher the autogenous shrinkage after 1 year. The total shrinkage, drying plus autogenous, of concrete containing slag was lower than 100% portland cement concrete [5].
7. Alkali-Silica Reactions (ASR)
GGBFS has been known to reduce the degree of which ASR occurs in concrete. The alkali in cement is used by the GGBFS during hydration which prevents the alkali from reacting with the potential deleterious aggregates. In addition, GGBFS typically reduces the permeability of the concrete which in turn prevents the alkalis form migrating through the pores [6]. MIAN FARID YOUSAF
Managing Director
Cell # 0300-5522467
Phone/Fax # 05827-448348
E-mail [email protected]
Allam Iqbal Road, Mirpur, Azad Kashmir
