EFFECT OF SILICA FUME ON HYDRATION HEAT AND STRENGTH DEVELOPMENT OF HIGH STRENGTH CONCRETE

Size: px

Start display at page:

Download "EFFECT OF SILICA FUME ON HYDRATION HEAT AND STRENGTH DEVELOPMENT OF HIGH STRENGTH CONCRETE"

Bryce Shields
6 years ago
Views:

1 CD EFFECT OF SILICA FUME ON HYDRATION HEAT AND STRENGTH DEVELOPMENT OF HIGH STRENGTH CONCRETE 1 M. Nili, A. Ehsani 2 1 Ass. Professor, Civil Eng. Dept. Faculty of Eng. Bu Ali Sina University, Hamedan, I.R.Iran 2 Msc Student, Civil Eng. Dept. Bu Ali Sina University, Hamadan, I.R.Iran ABSTRACT Recently, silica fume became a vital ingredient for producing concrete in aggressive hot climate of Iran. In mass structures heat generation due to hydration of cement and strength properties are two important parameters which affect service life of structures. In the early age the in the body of mass concrete is high and tensile strength is low. This special condition may lead to occurrence of thermal cracks. In the present study, concrete specimens with water cement ratio 0.3, were made and 0, 10 and 15 percent Portland cement replaced with silica fume. Temperature rise of the specimens was monitored just after casting in a semi adiabatic box. Temperature rise was recorded for 7 days. Furthermore, compressive strength of the cubic specimens from 1 day after casting to 91 days was measured. The results declared that hydration heat regime is affected by silica fume percent. The mixes with both 10 and 15% silica fume, had peak about 6ºC lower than the specimens without silica fume. Furthermore, peak of the specimens without silica fume occurred 23 hours after casting, while it became about 31 hours for silica fume specimens. The slope of cooling zone of hydration regime in the specimens with 10% silica fume is very mild compare with the others. On the other hand, 10% silica fume enhanced compressive strength more effectively. These results demonstrated that hydration heat and strength development of mass concrete are affected by silica fume content and higher replacement of this pozzolan material may adversely affect service life of structures. Keywords: silica fume, hydration heat, high strength concrete, strength development 1. INTRODUCTIONS Strength development of high strength concrete in the body of large mass concrete structures is effectively influenced by rising due to hydration heat. Normally, cement content of high strength concrete is high, therefore in the body of mass structures increase more rapidly and may adversely affect properties of concrete at early or later ages [1]. In addition, the characteristics of heat development such as peak, the time at which peak occur, slope gradient in heating or cooling zone and the remaining time at peak can be responsible for concrete properties in body of large mass concrete[2]. However,

2 134 / Effect of Silica Fume on Hydration Heat and. nowadays the consulting have no especial considering to a fact that reality of concrete properties in the center of structure is completely different with that named as standard specimens [3]. 2. MATERIALS AND TESTING PROGRAM Crushed stone, with 19 mm maximum nominal size, in two ranges of 5-10 and with relative density at saturated surface dry of 2.61 were used. Fineness modulus of sand and relative density were 3.24 and of 2.56 respectively. Absorption value is 3.09 and 2 for fine and coarse aggregate. The cement used was Portland cement Type 2, with a specific gravity of 3.11 and 3750 cm 2 /gr surface area. A commercial carboxylic type placticizer, (Gelenium 110M), was used to maintain workability of fresh concrete. Silica fume, made by Semnan Ferro Alley factory, was used at 0%, 5% and 10% (by weight) as partial replacement of cement. The characteristics of silica fume are given in Table 1. Mix proportions of the concrete are given in Table 2. Water-cementitious material (w/cm) ratio is 0.3. A pan mixer was used and the mixing procedures are as follows. First, sand and cement were placed and 50% mixing water and half admixture were added and mixed for 1 minute. The remaining water and admixture and coarse aggregate were together added and mixed 2 minutes. Table 1. Chemical composition of silica fume Composition Percent Al 2 O SiO Fe 2 O C CaO MgO Table 2. Mix proportions of the Concrete Material SF0.D SF10.D SF15.D Cement Water Fine agg Coarse agg. * (5-10 mm) Coarse agg. (10-19mm) Micro silica Super plasticizer Water/Cementitious material Slump * Aggregate in saturated surface dry condition

3 3 rd International Conference on Concrete & Development / EXPERIMENT RESULTS 3.1. Compressive Strength Strength development of the concrete mixtures versus age is shown in Figure 1. As it is shown from the early to later ages, compressive strength of the specimens with 10% silica fume is highest compare with two other specimens. However, as silica fume content increased to 15% rate of strength development in the early age was slow but, in the later ages of 28 and 90 days compressive strength of SF15 became higher than SF0. This may be attributed to the fact that in the early age, production of cement hydration, Ca(OH) 2, is not enough for activation of 15% silica fume. However, 10% silica fume may be an optimum value for cement replacement in the predetermined water cement ratio Com. St. (Mpa) Age(days) SF0 SF10 SF15 Figure 1. Strength development of the concrete mixtures 3.2. Hydration Heat Development Temperature rising of the specimens after casting was monitored and is demonstrated in Figure 2. It is shown that regime of hydration heat in silica fume specimens is different compare with the specimens without silica fume. Temperature rising curve during early age hydration can be divided in 4 following pattern: 1: slope of heating zone 2: peak value 3: time of peak 4: cooling zone slope For the silica fume specimens SF10 and SF15, slope of heat zone decreased compare with SF0. Furthermore peak diminished about 8 to 10 C for 15% and 10% cement replacement. Occurrence of peak postponed for silica fume specimens. An interesting result is that a mild slope is seen in cooling zone for silica fume specimens (Tables 3 and 4). This mild slope is desirable for lower thermal gradient.

4 136 / Effect of Silica Fume on Hydration Heat and. Figure 2. Temperature rising during hydration process Table 3. Peak, heating and cooling slope of the hydration heat curves Peak. 95% peak. angle of tangent in increasing (degree) angle of tangent in decreasing (degree) slope of tangent (G 1 ) slope of tangent (G 2 ) SF0.D SF10.D SF15.D Table 4: Net peak and time of peak for the mixtures Initial Temperature Occurrence of Peak Temperature Concrete Ambient Concrete Ambient Time after casting (min) Time after casting (hr) Maximum net rise. SF0.D SF10.D SF15.D CONCLUSIONS From the present study the following conclusions can be drawn:

5 3 rd International Conference on Concrete & Development / % silica fume enhanced compressive strength of the concrete with 0.3 water cement ratio from early to later ages. - Increasing silica fume content in the specimens did not lead to higher strength. - Curve of rising versus age was changed as cement was replaced with silica fume as follows: - Peak decreased about 5 C, - peak postponed, - Slope of heating and cooling zone became mild; this may lead to a desirable low thermal gradient in mass concrete. REFERENCES 1. Sioulas, B., Sanjayan, J. G., 2000, Hydration Temperatures in Large High- Strength Concrete Columns Incorporating Slag, Cement and Concrete Research, 2000, Vol. 30, pp Khan, A. A., Cook, W. D., Mitchell, D., 1995, Early age Compressive Stress- Strain Properties of Low-Medium, and High-Strength Concretes, 1995, ACI Material Journal, November-December 1993, Vol. 92, NO.6, pp Cook, W. D., Miao, B., Aitcin, P., Mitchell, D., 1992, Thermal Stresses in Large-Strength Concrete Columns, ACI Material Journal, January-February 1992, Vol. 89, NO.1, pp Carlson, R. W., Donald, L. H., Polivka, M., 1979, Causes and Control of Cracking in Unreinforced Mass Concrete, ACI Journal, July 1979, pp

A Study on the Influence of Mineral Admixtures in Cementitious System Containing Chemical Admixtures

International Journal of Engineering Research and Development e-issn: 2278-067X, p-issn: 2278-800X, www.ijerd.com Volume 10, Issue 3 (March 2014), PP.76-82 A Study on the Influence of Mineral Admixtures