**2.3 Effect of temperature on durability of slag concrete, fly ash concrete, and silica fume concrete**

During the production of cement, a significant quantity of CO2 is released into the atmosphere. It is estimated that the production of each ton of portland cement releases approximately 1 ton of CO2 gas. The world production of clinker accounts for about 7% of the total CO2 emissions. The use of these additions as cement replacement decreases the amount of clinker required, resulting in a limiting gas emissions of CO2 and dust in the atmosphere. The cement replacement does not only reduce the production costs but also address some environmental issues providing the enhanced concrete performances (better workability, lower hydration heat, and good durability) [19].

High-performance concrete (HPC) has been used more widely in recent years due to the increasing demand for durable concrete, thus to extend service life and reduce maintenance fee of concrete structures. HPC is known as a concrete which has a compressive strength over 60 MPa [20]. The pozzolana addition influences positively the compressive strength that could be easily increased up to 150 MPa. Pozzolanic materials are very important in the production of HPC. Further, HPC may contain materials such as silica fume, fly ash, ground granulated blast-furnace slag, natural pozzolana, chemical admixtures, and other materials, individually or in various combinations.

In slag cements, clinker is the principal activator of the binder. However, the first produced hydrates will be those of the clinker; C-S-H and Ca(OH)2 uniformly cover the grains with the slag and the clinker; there after the lime excess activates the hydration of the slag with a texture of C-S-H similar to that of cements; it results in calcium silicate hydrates and hydrated tetra-calcium aluminates. Other research undertaken on the subject reported that the more fine the slag is, the better is its performance [21].

Tebbal's research indicated that the compressive strength is higher, when the cement is replaced by 5% silica fumes mainly, the combined mixture of 5% of silica fume and 10% of slag, at a maximum value of 170 MPa [22].

During the hydration reaction between portland cement and water, a cementitious gel and lime are formed. Pozzolanic materials react with this lime in the presence of moisture to form additional cementitious gel. Slags also submit to this pozzolanic reaction. This reaction leads to a reduction in the permeability of the concrete and an increase in its strength [23].

Traditionally, slag, silica fume, and fly ash were used in concrete individually. Nowadays, due to the improved access to these materials, concrete producers can combine two or more of such materials to optimize concrete properties at fresh state (workability) and hardened state (strength and durability); a reduction in the rate of penetration of chloride ion concrete reduced the potential of chloride-induced corrosion [20].

Ravindrarajah et al. stated that concrete consists of discrete and interconnected pores of a variety of sizes and shapes and their distribution depends on the binder material type. The refinement of pore size as well as grain size of concrete is attained by the use of fly ash, slag, and silica fume due to its fineness, pozzolanic, and cementitious property. Free water in the gel causes capillary cavities, and combined water in hardened cement paste improves the hydration process. Combined water can be dehydrated at 1000°C only due to its stability [24].

**109**

*Mechanical Behavior of High-Performance Concrete under Thermal Effect*

color resembles the degradation of cement paste properties [25].

above 210°C, and loss in compressive strength was 8% [27].

According to Bingöl et al., there are no significant losses in the compressive strength of lightweight aggregate concrete observed between 150 and 300°C. The initial strength loss is important for all mix groups at 750°C. The heating duration does not affect the strength loss significantly, but high temperature is a significant parameter of strength loss. Stephen S. Szoke stated the degradation of pavement

The effect of thermal cycles on the compressive strength of high-volume fly ash concrete has been studied by Srinivasa Rao et al. They are confirmed that the structural elements when exposed to solar radiation, the thermal gradients in the elements are influenced by the degree of humidity. In that way the elements of structures undergo one thermal cycle per day and also are exposed to peak value of

Noumowé mentioned that thermal gradients were very significant and generating high compressive stresses at the specimen surface during the heating tests at 210 and 310°C. This thermal loading causes stresses which are accompanied by the degradations of cement paste due to abrupt changes in volume further leading to a damage of the concrete. Contrasting conditions observed while cooling the temperature in the center of specimen are more in the surface. This condition causes compressive stresses at the center and tensile stresses on the surface. Compressive strength is decreased with the increase in temperature. However, losses were very less between 20 and 110°C. There was an appreciable reduction in the strength

Falade concluded that the compressive strength of concrete is reduced with increase in water/cement ratio and increase in temperature but increased with increase in curing period. The bond between the concrete within matrix decreases as the temperature increases. The loss in strength of specimens is in between 24 and 40% at a maximum temperature of 800°C/h., which is influenced by the mix proportion and curing age. Lightweight concrete consists of periwinkle shells which are the only appropriate material for structures that will be exposed to temperature lower than 300°C [28]. Siddique et al. concluded that concrete with GGBFS can be used in constructions exposed to elevated temperatures. The degradation of mechanical properties of concrete is less between 27 and 100°C. The values of compressive strength, split tensile strength, and modulus of elasticity are reduced lower than 40% after exposing to a temperature more than 350°C. The loss in mass is not very important at temperatures between 200 and 350°C. GGBFS may contribute to some extent to the residual compressive strength of concrete at elevated temperatures. Similar findings

Pathan et al. stated that in practice, at a temperature of 250°C, calcium hydroxide starts to dehydrate generating more amount of water vapor. Further, significant reduction in their compressive strength was observed at temperatures in the range

Seshagiri Rao et al. stated that a considerable change in physical structure and chemical composition appears when concrete is exposed to high temperature. Above 100°C, dehydration of water in C-S-H gel is important. This is added to thermal expansion of aggregates which causes the increase in internal stresses at 300°C, and further microcracks are developed. Ca(OH)2, the product of hydration of cement paste, separates into

Chowdhury stated that at high temperatures, the loss in compressive strength and tensile strength was observed for all three concrete mixes of 100, 80, and 40 MPa. The loss in strength for 80 MPa mix was about 44% when exposed to 400°C for 12 h. At 60°C, the loss in tensile strength for 80 MPa mix was about 18% for 72 h of exposure. A nonlinear relationship was observed between weight loss and maximum temperature, but loss was least in the case of the highest strength

CaO and H2O at 400–600°C subsequently; shrinkage of concrete occurs [31].

*DOI: http://dx.doi.org/10.5772/intechopen.89916*

heating period and cooling period [26].

were observed by Siddique and Kaur [29].

of 300 and 600°C [30].

*Compressive Strength of Concrete*

**silica fume concrete**

heat, and good durability) [19].

in various combinations.

performance [21].

corrosion [20].

permeability is an important characteristic of durable concretes and may be obtained by lowering the water/cementitious material ratio (W/C) and using pozzolans (fly ash and silica fume) or slag as a portion of the cementitious material [15, 18].

**2.3 Effect of temperature on durability of slag concrete, fly ash concrete, and** 

During the production of cement, a significant quantity of CO2 is released into the atmosphere. It is estimated that the production of each ton of portland cement releases approximately 1 ton of CO2 gas. The world production of clinker accounts for about 7% of the total CO2 emissions. The use of these additions as cement replacement decreases the amount of clinker required, resulting in a limiting gas emissions of CO2 and dust in the atmosphere. The cement replacement does not only reduce the production costs but also address some environmental issues providing the enhanced concrete performances (better workability, lower hydration

High-performance concrete (HPC) has been used more widely in recent years due to the increasing demand for durable concrete, thus to extend service life and reduce maintenance fee of concrete structures. HPC is known as a concrete which has a compressive strength over 60 MPa [20]. The pozzolana addition influences positively the compressive strength that could be easily increased up to 150 MPa. Pozzolanic materials are very important in the production of HPC. Further, HPC may contain materials such as silica fume, fly ash, ground granulated blast-furnace slag, natural pozzolana, chemical admixtures, and other materials, individually or

In slag cements, clinker is the principal activator of the binder. However, the first produced hydrates will be those of the clinker; C-S-H and Ca(OH)2 uniformly cover the grains with the slag and the clinker; there after the lime excess activates the hydration of the slag with a texture of C-S-H similar to that of cements; it results in calcium silicate hydrates and hydrated tetra-calcium aluminates. Other research undertaken on the subject reported that the more fine the slag is, the better is its

Tebbal's research indicated that the compressive strength is higher, when the cement is replaced by 5% silica fumes mainly, the combined mixture of 5% of silica

During the hydration reaction between portland cement and water, a cementi-

Traditionally, slag, silica fume, and fly ash were used in concrete individually. Nowadays, due to the improved access to these materials, concrete producers can combine two or more of such materials to optimize concrete properties at fresh state (workability) and hardened state (strength and durability); a reduction in the rate of penetration of chloride ion concrete reduced the potential of chloride-induced

Ravindrarajah et al. stated that concrete consists of discrete and interconnected pores of a variety of sizes and shapes and their distribution depends on the binder material type. The refinement of pore size as well as grain size of concrete is attained by the use of fly ash, slag, and silica fume due to its fineness, pozzolanic, and cementitious property. Free water in the gel causes capillary cavities, and combined water in hardened cement paste improves the hydration process. Combined

tious gel and lime are formed. Pozzolanic materials react with this lime in the presence of moisture to form additional cementitious gel. Slags also submit to this pozzolanic reaction. This reaction leads to a reduction in the permeability of the

fume and 10% of slag, at a maximum value of 170 MPa [22].

water can be dehydrated at 1000°C only due to its stability [24].

concrete and an increase in its strength [23].

**108**

According to Bingöl et al., there are no significant losses in the compressive strength of lightweight aggregate concrete observed between 150 and 300°C. The initial strength loss is important for all mix groups at 750°C. The heating duration does not affect the strength loss significantly, but high temperature is a significant parameter of strength loss. Stephen S. Szoke stated the degradation of pavement color resembles the degradation of cement paste properties [25].

The effect of thermal cycles on the compressive strength of high-volume fly ash concrete has been studied by Srinivasa Rao et al. They are confirmed that the structural elements when exposed to solar radiation, the thermal gradients in the elements are influenced by the degree of humidity. In that way the elements of structures undergo one thermal cycle per day and also are exposed to peak value of heating period and cooling period [26].

Noumowé mentioned that thermal gradients were very significant and generating high compressive stresses at the specimen surface during the heating tests at 210 and 310°C. This thermal loading causes stresses which are accompanied by the degradations of cement paste due to abrupt changes in volume further leading to a damage of the concrete. Contrasting conditions observed while cooling the temperature in the center of specimen are more in the surface. This condition causes compressive stresses at the center and tensile stresses on the surface. Compressive strength is decreased with the increase in temperature. However, losses were very less between 20 and 110°C. There was an appreciable reduction in the strength above 210°C, and loss in compressive strength was 8% [27].

Falade concluded that the compressive strength of concrete is reduced with increase in water/cement ratio and increase in temperature but increased with increase in curing period. The bond between the concrete within matrix decreases as the temperature increases. The loss in strength of specimens is in between 24 and 40% at a maximum temperature of 800°C/h., which is influenced by the mix proportion and curing age. Lightweight concrete consists of periwinkle shells which are the only appropriate material for structures that will be exposed to temperature lower than 300°C [28].

Siddique et al. concluded that concrete with GGBFS can be used in constructions exposed to elevated temperatures. The degradation of mechanical properties of concrete is less between 27 and 100°C. The values of compressive strength, split tensile strength, and modulus of elasticity are reduced lower than 40% after exposing to a temperature more than 350°C. The loss in mass is not very important at temperatures between 200 and 350°C. GGBFS may contribute to some extent to the residual compressive strength of concrete at elevated temperatures. Similar findings were observed by Siddique and Kaur [29].

Pathan et al. stated that in practice, at a temperature of 250°C, calcium hydroxide starts to dehydrate generating more amount of water vapor. Further, significant reduction in their compressive strength was observed at temperatures in the range of 300 and 600°C [30].

Seshagiri Rao et al. stated that a considerable change in physical structure and chemical composition appears when concrete is exposed to high temperature. Above 100°C, dehydration of water in C-S-H gel is important. This is added to thermal expansion of aggregates which causes the increase in internal stresses at 300°C, and further microcracks are developed. Ca(OH)2, the product of hydration of cement paste, separates into CaO and H2O at 400–600°C subsequently; shrinkage of concrete occurs [31].

Chowdhury stated that at high temperatures, the loss in compressive strength and tensile strength was observed for all three concrete mixes of 100, 80, and 40 MPa. The loss in strength for 80 MPa mix was about 44% when exposed to 400°C for 12 h. At 60°C, the loss in tensile strength for 80 MPa mix was about 18% for 72 h of exposure. A nonlinear relationship was observed between weight loss and maximum temperature, but loss was least in the case of the highest strength

#### *Compressive Strength of Concrete*

mix for every temperature and duration of high temperature exposure. An easy way to comply with the conference paper formatting requirements is to use this document as a template and simply type your text into it [32].

According to Santosh Kumar et al. [33], the materials like pozzalonas may be natural and artificial like industrial wastes or by-products which require less energy to make fine particles. These materials exhibit cementitious properties and combine with calcium hydroxide producing cementitious material [34].

Gowri et al. presents the results of experimental studies conducted on performance of High Volumes of Slag Concrete (HVSC) exposed to elevated temperatures up to 600°C. In HVSC, 50% of cement is replaced with Ground Granulated Blast Furnace Slag (GGBS). In this experimental studies, HVSC of 100 mm cubes are cast and tested for various water/binder ratios ranging from 0.55 to 0.27. The specimens are exposed to elevated temperatures of 200°C, 400°C and 600°C for 4, 8, 12 hours. Result of compressive strengths and weights of cubes after expose to high temperature are estimated. Percentage loss in compressive strengths and weights are also evaluated. The results illustrate that the loss in compressive strength and weights are more for higher temperatures for longer duration for higher water/binder ratios [35].

According to Jawed et al., percentage loss of compressive strength is higher with an increase amount of fly ash in concrete samples, i.e., for 20% fly ash concrete. This is due to high impermeability and moisture gained in longer curing period resulting in high pore pressure but low initial strength gain [36].

In 2004, Yüzer et al. carried out a study on the effects of fire, and extinguishing on the properties of concrete, mortars with and without silica fume were exposed to different temperatures, such as 100, 200, 300, 600, 900, and 1200°C and cooled slowly in the air and fast in water in two groups. Flexural and compressive strength tests were performed on the samples which were cooled up to room temperature, and changes in compressive strength in color were determined by Munsell color system. High temperature has caused damages to decrease in mechanical strengths at 600°C. Researchers observed that the changes in color hue component and the compressive strength have similarities. Test results show that residual color changes in mortar can give an idea about the effect of high temperatures on mechanical properties of mortar during a fire [37].

Ahmad's research includes an experimental investigation to study the effect of high temperatures on the mechanical properties of concrete containing admixtures. A comparative study was conducted on concrete mixes, reference mix without an additive, and that with an admixture. Concrete was exposed to three levels of high temperatures (200, 400, 600°C), for duration of 1 h, without any imposed load during the heating. Super plasticizer, plasticizer, retarder, water-reducing admixture, an accelerator, and an air entraining admixture, five types of admixtures, were used. Mechanical properties of concrete were studied at different high temperatures, including compressive strength, splitting tensile strength, modulus of elasticity, and ultimate strain. Test results showed a reduction in the studied properties by different rates for different additives, and for each temperature, the decrease was very limited at a temperature up to 200°C but was clear at 400–600°C [38].
