Effect of cooling technique of blast furnace slag on the thermal behavior of solid cement bricks

Accepted Manuscript Effect of Cooling Technique of Blast Furnace Slag on the Thermal Behavior of Solid Cement Bricks Dina M. Sadek PII:

S0959-6526(14)00501-0

DOI:

10.1016/j.jclepro.2014.05.033

Reference:

JCLP 4326

To appear in:

Journal of Cleaner Production

Received Date: 10 May 2013 Revised Date:

21 April 2014

Accepted Date: 11 May 2014

Please cite this article as: Sadek DM, Effect of Cooling Technique of Blast Furnace Slag on the Thermal Behavior of Solid Cement Bricks, Journal of Cleaner Production (2014), doi: 10.1016/ j.jclepro.2014.05.033. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Effect of Cooling Technique of Blast Furnace Slag on the Thermal Behavior of Solid Cement Bricks

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Author: Dina M. Sadek Affiliation : Building Materials Research and Quality Control Institute, Housing and Building National Research Center

Tel. : Country code: +20

area code: 02

E-mail: [email protected]

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Corresponding Author: Dina M. Sadek

tel. number:33356722

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Address: 87 El-Tahrir St., Dokki, Giza, Egypt

Abstract

Sustainable construction has become a challenge in the engineering community. Some of the important elements in this respect are the reduction of the consumption of

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energy and natural resources. Big attention is being focused on the recycling of wastes/by-products to produce more sustainable building materials. Blast furnace slag (BFS) is a by-product generated from the production of pig iron in the blast furnace. In Egypt, there are two main types of BFS depending on the used cooling technique;

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air-cooled slag (ACS) produced by slow cooling of BFS under atmospheric conditions and water-cooled slag (WCS) produced by water quenching. This paper examines the

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effect of using ACS and WCS without any processing to substitute natural sand (NS) in solid cement bricks. The behavior of the bricks was evaluated at ambient temperature and after exposure to elevated temperatures up to 800 °C. Five mixes were prepared: M1 is the control mix without sand substitution, M2 and M3 are mixes including 50% and 100% replacement of sand with ACS, respectively. Mixes M4 and M5 contain 50% and 100% replacement of sand with WCS, respectively. Results indicate the possibility of recycling ACS and WCS, without processing to conserve energy, as fine aggregate in bricks manufacturing. The use of ACS resulted in a higher deterioration after exposure to elevated temperatures, although it increased the compressive strength of the unheated specimens. On the other hand, the bricks containing WCS are thermally more stable than NS and ACS bricks.

ACCEPTED MANUSCRIPT Keywords: Sustainable construction; Blast furnace slag; Cooling technique; Solid

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cement bricks; Compressive strength.

ACCEPTED MANUSCRIPT Effect of Cooling Technique of Blast Furnace Slag on the Thermal Behavior of Solid Cement Bricks

Abstract

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Sustainable construction has become a challenge in the engineering community. Some of the important elements in this respect are the reduction of the consumption of energy and natural resources. Big attention is being focused on the environment by safeguarding of natural resources and recycling of wastes/by-products to produce more sustainable building

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materials. Blast furnace slag (BFS) is a by-product generated from the production of pig iron in the blast furnace. In Egypt, there are two main types of BFS depending on the cooling

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technique; air-cooled slag (ACS) produced by slow cooling of BFS under atmospheric conditions and water-cooled slag (WCS) produced by water quenching. ACS is currently recycled as coarse aggregate and fine fractions are dumped, while WCS is recycled after grinding, which consumes a lot of energy. This paper examines the effect of using ACS and WCS without any processing to substitute natural sand (NS) in solid cement bricks. The

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behavior of the bricks was evaluated at ambient temperature and after exposure to elevated temperatures up to 800 °C. Five mixes were prepared: M1 is the control mix without sand substitution, M2 and M3 are mixes including 50% and 100% replacement of sand with ACS, respectively. Mixes M4 and M5 contain 50% and 100% replacement of sand with WCS,

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respectively. Results indicate the possibility of recycling ACS and WCS, without processing to conserve energy, as fine aggregate in bricks manufacturing. The use of ACS resulted in a

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higher deterioration after exposure to elevated temperatures, although it increased the compressive strength of the unheated specimens. On the other hand, the bricks containing WCS are thermally more stable than NS and ACS bricks.

Keywords: Sustainable construction; Blast furnace slag; Cooling technique; Solid cement bricks; Compressive strength.

1. Introduction Blast furnace slag (BFS) is a nonmetallic by-product obtained as a molten stream at a

ACCEPTED MANUSCRIPT temperature of 1400-1600 °C during the production of pig iron in the blast furnace, a stage process in the production of steel. BFS consists principally of silicates and alumino-silicates of calcium (Oss, 2002; Shi and Qian, 2000; Zeghichi, 2006). Significant quantities of BFS are generated every day from steel industries. Approximately 300 kg of BFS are generated per ton

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of pig iron and more than 167 million tons of BFS were produced worldwide in 1996 (Garcia et al., 2009). It is estimated that annual world iron slag output in 2012 was approximately 270 to 320 million tons, based on typical ratios of slag to crude iron output (Oss, 2013). The cooling process of BFS is responsible for generating different types of slags. Although, the

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chemical composition of solidified BFS may remain unchanged, its physical attributes glassy or stony, compact or vesicular - vary widely with the changing process of cooling. The

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cooling technique also determines the uses of slag (Indian Minerals Yearbook, 2012; Oss, 2002; Zeghichi, 2006). In Egypt, BFS is normally produced in two forms depending on the cooling technique as will be described.

When the molten slag is allowed to cool slowly under ambient conditions, it solidifies into a gray, crystalline, hard and stone-like material known as air-cooled slag (ACS). ACS is a

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stable solid consists of crystallized Ca-Al-Mg silicates, especially gehlenite (C2AS) and akermanite (C2MS2). Thus, ACS has no or very little cementing properties, but exhibits mechanical properties similar to crushed stone. After crushing to aggregate sizes, ACS can be used as coarse aggregate for asphaltic paving, railway ballast, road bases and sub-bases, and

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concrete (Das et al., 2007; Demirboğa and Gül, 2006; Galal et al, 2004; Indian Minerals Yearbook, 2012; Kalalagh et al., 2005; Oss, 2002; Shi and Qian, 2000; Shoaib et al., 2001;

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Slag Cement Association, 2003; The Japan Iron and Steel Federation, 2006; Zeghichi, 2006). ACS exhibits favorable mechanical properties for aggregate use including good abrasion resistance, high bearing strength, high resistance to weathering action such as freezing and thawing, and low sulfate soundness losses. The asphalt containing ACS aggregate has good binding, impermeability to humidity, high resistance to stripping, high skid resistance and increased rutting resistance, which are advantageous for highways, industrial roads and parking areas subjected to heavy axial loads. It is recommended to use at least 50% of ACS in asphalt mixtures for heavy traffic roads (Kalalagh et al., 2005). Furthermore, concrete containing ACS aggregate was found to have higher or similar strength, lower drying

ACCEPTED MANUSCRIPT shrinkage and creep compared with the control concrete made from natural aggregate (Cement Concrete and Aggregates, 2008). Sadek and El-Attar (2012) investigated the possibility of recycling ACS as a substitute of natural coarse aggregate on the strength and durability of high performance concrete. It was reported that the compressive strength and

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abrasion resistance of concrete containing 100% ACS increased by 18% and 15%, respectively compared with the control concrete. Furthermore, ACS concrete has a good resistance to sulfate attack up to one year.

On the other hand, when the molten slag is cooled very rapidly by quenching using water

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jets, it solidifies into a glassy and granular form to produce a sand-like product known as water-cooled slag (WCS). WCS consists of vitreous Ca-Al-Mg silicate with a cellular and

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almost non-crystalline structure. Due to its high content of silica and alumina in an amorphous state, finely ground WCS has latent hydraulic cementitious properties similar to that of natural pozzolans, fly ash and silica fume. Hence, WCS has been widely utilized after being ground to a suitable fineness as a supplementary cementing material (Atiş and Bilim, 2007; Cement Concrete and Aggregates, 2008; Galal et al, 2004; Indian Minerals Yearbook,

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2012; Oss, 2002; Shi and Qian, 2000; Shoaib et al., 2001; Slag Cement Association, 2003; The Japan Iron and Steel Federation, 2006; Yüksel and Genç, 2007). It has been proved that around 50% of clinker could be replaced by water-cooled slag in the production of slag cement, which has low heat of hydration, low alkali aggregate reaction, high resistance to

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chlorides and sulfate (Das et al., 2007; Indian Minerals Yearbook, 2012). According to Laakri et al. (2014), using of WCS tends to reduce the water demand and so increases the fluidity of

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pastes for the same water to solid ratio. The replacement of cement by WCS induced a significant decrease in the shrinkage. The 28-days total shrinkage of mortar decreased by 69% by replacing 30% of cement by WCS. Furthermore, it is demonstrated that concrete containing WCS as a mineral additive has higher workability, reduced bleeding, reduced heat of hydration, similar or even superior long-term strength, reduced permeability and chlorideion penetration, and improved resistance to chemical attack compared with concrete containing only Portland cement (Aldea et al., 2000; Atiş and Bilim, 2007; Barnett et al., 2006; Berndt, 2009; Jariyathitipong et al., 2012; Khatib and Hibbert, 2005; Osborne, 1999; Yeau and Kim, 2005). Khatib and Hibbert (2005) investigated the influence of replacing 0-

ACCEPTED MANUSCRIPT 80% of cement with ground WCS on concrete strength. The use of WCS reduced concrete strength and modulus of elasticity during the first 28 days. Beyond that, the strength increased with the presence of WCS up to 60% replacement. On the other hand, Aldea et al. (2000) reported a little effect of slag replacement up to 50% upon concrete strength, whereas higher

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replacement results in a drop in compressive strength. The use of slag had a beneficial effect of decreasing the chloride permeability and penetrability, and the effect increases significantly by increasing slag replacement. It should be noted that the reactivity of WCS is strongly influenced by its fineness. The surface area required for WCS as a cementitious material is

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normally greater than that for cement; a range of 550–650 m2/kg is accepted. However, the grinding resistance of WCS is higher than that of cement, thus grinding WCS to the

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mentioned levels is expensive in addition to be a time and energy consuming process (Garcia et al., 2009).

Despite all the described potential uses of slag, significant amounts of BFS, especially fine ACS, are dumped causing adverse impact on the environment. Recycling of BFS without processing as fine aggregate is an attractive alternative to disposal of fine fractions of ACS

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and consumption of energy for grinding WCS. Although some researches investigated the utilization of slag as fine aggregate in construction, there is no available data about the effect of using slag as fine aggregate in solid cement bricks, especially after exposure to elevated temperatures, although the mix proportions and manufacturing method for solid cement bricks

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are different from those for mortar and concrete. This paper investigates the potential of recycling ACS and WCS, without any processing, as fine aggregates in the production of solid

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cement bricks to be used as load bearing and non-load bearing units. Either ACS or WCS was used to replace 0, 50 and 100% of natural sand and the effect of cooling technique of BFS on the behavior of solid cement bricks at ambient temperature and after exposure to elevated temperatures up to 800 °C was investigated.

2. Materials and Methods 2.1 Materials The cement used throughout this program was designated as CEM I 42.5 N according to EN 197-1:2000. Crushed dolomite with a nominal maximum size of 14 mm, specific gravity

ACCEPTED MANUSCRIPT and water absorption of 2.70 and 0.97%, respectively was used as coarse aggregate and natural sand (NS) with specific gravity of 2.5 was used as fine aggregate. Two types of blast furnace slags (BFS) produced from the same furnace, but differ in their rate of cooling namely; ACS and WCS were used as alternative fine aggregates. They were obtained from

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Iron and Steel Company, Egypt and used as received from the factory without any processing and only coarse particles were separated by sieving on a 4.75 mm sieve to obtain the fine fractions of slag. The chemical composition of BFS was determined by XRF apparatus. BFS primarily consists of SiO2, Al2O3, and CaO, and MgO (Table 1). ACS contains mainly

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crystalline phases such as Akermanite peaks "1" (calcium-magnesium-silicate), Gehlenite peaks "2" (calcium-alumino-silicate), Quartz peaks "3" (low temperature phase of SiO2), and

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minor Calcite peaks "4", while WCS is a vitreous material with an amorphous hump characteristic of the glass and no peaks attributed to any crystallized compound can be identified due to the rapid quenching process (Fig. 1). The physical properties (i.e., specific gravity, unit weight, clay and fine materials, and grading) of fine aggregates were determined according to ASTM C128-07, ASTM C29/C29M-07, ASTM C117-04 and ASTM

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C136-05, respectively and are shown in Table 2 and Fig. 2. It can be observed that WCS is coarser than ACS and NS. This is due to the granulation of WCS.

2.2 Methods

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Two series of mixes were prepared in addition to the control mix made with NS. The first series (mixes 2 and 3) contained ACS, while the second series (mixes 4 and 5) contained

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WCS. In each series, slag was used to replace 50% and 100% of NS based on the weight basis. All mixes were designed using the absolute volume method. The cement content and coarse to fine aggregate ratio were 200 kg/m3 and 1.5, respectively. The proportions of the mixes are presented in Table 3. All mixes were designed to be semi-dry to avoid sagging after the removal of the mould. Due to the higher water absorption, angular appearance and surface roughness of both ACS and WCS compared with NS, extra water was added to keep the workability constant. Moreover, mixes containing WCS needed more water than mixes containing ACS, which implies that WCS has a higher porous structure compared with ACS as it has a honeycombed structure due to its rapid quenching with water. Thus, the use of BFS

ACCEPTED MANUSCRIPT especially WCS as fine aggregate has a negative impact on the water demand of bricks especially for replacement ratios above 50%. Similar findings were reported by Nataraja et al. (2013) that the use of ground WCS at any level of replacement (i.e., 25, 50, 75 or 100%) to natural sand significantly reduces the flowability of cement mortar. The decrease in flow for

can be increased by adding superplasticiser.

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25% is marginal and for higher percentages, the flow decreases substantially. This flowability

The manufacturing process for solid cement bricks is different from that for concrete. From each mix, fifty specimens were prepared for the measurement of the physical and

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mechanical properties of bricks. Solid cement bricks of 250×120×60 mm size were manufactured by filling the press moulds with the fresh mix and consolidating the mix by

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rigorous vibration and direct pressure of 20 MPa. The bricks were then quickly removed from the moulds and left in laboratory conditions for 24 hours then cured by water sprinkling twice per day. Fig. 3 shows the bricks just after pressing.

After 28 days of curing, the specimens were left to dry in air for 2 days before heating. The specimens were divided into four groups; each group was placed in an electric furnace

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with temperature capacity of 1000 °C, heated to an identical temperature (i.e., 200, 400, 600 and 800 °C) at a heating rate of 5 °C/min. Each temperature was maintained for 2 h to achieve the thermal steady state. The specimens were allowed to cool naturally in the furnace to room temperature to prevent thermal shock. Residual compressive strength, water absorption and

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unit weight were determined and compared with those of unheated specimens to quantify the deterioration of the bricks. Tests were carried out according to ASTM C 67-03. For each test,

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each result is the average of five measurements. The compression test was carried out using a Tinius Olsen testing machine with a maximum capacity of 2000 kN.

3. Results and Discussion

In the following sections, the effect of recycling ACS and WCS as fine aggregates in solid cement bricks will be illustrated and discussed.

3.1 Visual inspection By visually inspecting the bricks after exposure to elevated temperatures, it was observed

ACCEPTED MANUSCRIPT that up to 400 °C, the surface of the bricks was dense and intact without cracks. For ACS mixes, hair cracks appeared on the surface of the bricks after heating to 600 °C and more cracks occurred with the increase in ACS content. As the temperature increases, a network of intensive cracks was observed and most of ACS specimens were fully disintegrated at 800 °C

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(Fig. 4). Hence, the incorporation of ACS as fine aggregate accelerates the spread of cracking. On the other hand, only hair cracks were observed on the surface of WCS specimens heated at 800 °C (Fig. 4) indicating the stability of WCS bricks at elevated temperatures.

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3.2 Unit weight

The unit weight values for the manufactured solid cement bricks are shown in Fig. 5. At

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room temperature, there is an increase in the unit weight of bricks with increasing the replacement percentage of NS with ACS. Solid cement bricks containing 100% ACS showed the highest unit weight with an increase of 11% compared with NS bricks. On the other hand, the use of WCS did not cause substantial effect on the unit weight of the manufactured bricks even at high replacement levels. With up to 50% replacement, the unit weight was almost

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similar to that of the control, whereas at 100% replacement, a reduction of only 5.8% occurred. The difference in the unit weight can be attributed to the difference in the specific gravity of the used fine aggregates (low specific gravity of WCS and high specific gravity of ACS in comparison to NS). Considering the specimens exposed to elevated temperatures, a

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continuous reduction in the unit weight was noted with temperature. However, ACS bricks showed higher unit weight than WCS bricks at the same replacement percentage of NS.

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As shown in Fig. 5 and according to the classification set out in ASTM C 90-03 for solid cement bricks based on the unit weight, where I, II and III are the range of unit weight for normal weight, medium weight and lightweight bricks, respectively, it can be observed that all the manufactured bricks tested at room temperature or after exposure to 600 °C are classified as normal weight bricks, except those containing 100% WCS are classified as medium weight bricks. Exposure to 800 °C converted the bricks to the class of medium weight bricks.

3.3 Weight loss Concrete includes capillary water, physically absorbed water and chemically bound water

ACCEPTED MANUSCRIPT in cement hydrates such as C-S-H and Ca(OH)2. During heating, the cement paste dries and water is free to be driven out. Previous research acknowledges that the changes in the properties at high temperatures are related to the evaporation of water. The simplest way for assessing the moisture change during heating is monitoring the weight loss (Savva et al.,

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2005; Zhang et al., 2002). The weight loss is the difference between the specimen dry weight after and before exposure to elevated temperature divided its initial dry weight. Fig. 6 illustrates the weight loss of the bricks after heating. In general, the weight loss increases with temperature as follows: up to 200 °C, the weight loss is rather small indicating the departure

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of the free water from the capillary pores. Between 400 and 600 °C, a higher increase in the weight loss can be observed for all mixes. At 800 °C, a significant weight loss corresponding

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to 13.8% (in average) was observed owing to the release of chemically combined water from the cement hydrate (i.e., dehydration of cement hydrates) and the decomposition of aggregates at very high temperatures (Savva et al., 2005; Shoaib et al., 2001; Zhang et al., 2002). According to Kulkarni et al. (2012), that a weight loss of 6.36% was recorded for high performance concrete heated at 900 °C, and 58.41% of this weight loss occurs when exposed

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to 300 °C. The remaining 41.59% weight is lost gradually up to 900 °C. The use of WCS had a beneficial effect on the behavior of bricks especially after exposure to 600 and 800 °C. The weight loss of 50% WCS and 100% WCS bricks after exposure to 600 °C was 16% and 24% lower than that of NS bricks, while it was 17% and 19% lower than that

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of NS bricks after exposure to 800 °C. On the other hand, the use of ACS increased the weight loss of the bricks. The weight loss of 50% ACS and 100% ACS after exposure to 600 °C was

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13% and 65% higher than the corresponding NS bricks.

3.4 Water absorption

The absorption of the bricks gives an indirect measure of the pore structure and porosity which are the major reasons for the strength loss. Fig. 7 demonstrates the water absorption of solid cement bricks as a function of temperature. Water absorption increased by increasing the replacement percentage of NS by BFS, regardless of its cooling technique. This may be due to the increased amount of water added in mixes containing BFS as fine aggregate. Moreover, water absorption was also increased with temperature and this increase was more pronounced

ACCEPTED MANUSCRIPT at 800 °C as compared with 600 °C, which reveals the internal cracking by the decomposition of limestone. The increase in the water absorption with temperature may be due to the following reasons: (1) the generation of an additional void space in the heated specimens by the release of adsorbed water and bound water and the corresponding microstructural changes

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(i.e., dehydration of cement paste hydrates), (2) the formation and enlargement of microcracks leading to a sort of pores opening in the heated specimens (Fares et al., 2010; Saad et al., 1996). Lau and Anson (2006) found an increase in the porosity and pore size of concrete with temperature, irrespective of concrete strength.

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Evidently, NS bricks showed the lowest water absorption while WCS bricks had the highest water absorption, irrespective of temperature. Yüksel and Genç (2007) attributed the

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increased water absorption of WCS concrete to the formation of porous structure and generation of pores at the interface between the cement paste and WCS. Compared with the water absorption of unheated specimens, it can be found that the water absorption of NS, 100% ACS and 100% WCS bricks increased by 27%, 39% and 18%, respectively after exposure to 600 °C. After heating at 800 °C, the water absorption increased by 55% and 41% and

100% WCS

bricks,

respectively while ACS

bricks

were

almost

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for NS

disintegrate/damaged. Hence, although the use of WCS as fine aggregate increased the water absorption of bricks at ambient temperature, it had the lowest increase in absorption after exposure to elevated temperatures, indicating the resistance of WCS to elevated temperatures.

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On the other hand, ACS bricks showed the highest increase in the water absorption after heating, indicating the intensive cracking in ACS bricks.

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According to ASTM C 90-03 for load bearing units that the maximum permissible limit for solid cement bricks water absorption is 208 kg/m3, 240 kg/m3 and 288 kg/m3 for normal weight bricks, medium weight bricks and lightweight bricks, respectively. All the manufactured bricks satisfied the specification requirements for water absorption, regardless of exposure to elevated temperatures.

3.5 Compressive strength Fig. 8 shows the effect of temperature on the compressive strength of solid cement bricks. It is clear from the figure that the compressive strength of the unheated bricks and bricks

ACCEPTED MANUSCRIPT exposed to elevated temperatures up to 600 °C exceeded the minimum value of 13.1 MPa for load bearing units according to ASTM C 90-03, which indicate that the produced bricks can sustain elevated temperatures up to 600 °C as load bearing units, regardless of fine aggregate type. On the other hand, 50% WCS bricks can sustain elevated temperatures up to 800 °C as

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load bearing units. The type of fine aggregate has a significant effect on the compressive strength of the unheated specimens. At room temperature, the compressive strength increased by increasing ACS proportion. The use of 50% and 100% ACS increased the compressive strength of the

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bricks by 29% to 53%, respectively compared with NS bricks. This enhancement may be due to the roughness and angularity of ACS to form a strong bond characteristic between paste

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and ACS surface. Demirboğa and Gül (2006) reported that the compressive strength of ACS concretes was approximately 60–80% higher than that of control concretes for different w/c ratios. On the other hand, mixes containing WCS tended to have lower compressive strength than NS bricks. The use of 50% and 100% WCS decreased the compressive strength by 9% and 29%, respectively compared with NS bricks. Yüksel and Genç (2007) reported a 22.4%

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reduction in the compressive strength of concrete containing 50% of WCS as fine aggregate. The deficiency of unheated WCS bricks was put down to the weakness in WCS grains resulted from its honeycombed structure in addition to the significant amount of added water in mixes containing WCS. The highest and lowest compressive strength were noted in 100%

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ACS bricks and 100% WCS bricks, respectively. For the specimens exposed to elevated temperatures, it can be found that the behavior of

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the bricks differs depending on the temperature degree and the type of fine aggregate. For NS bricks, the heating regime can be divided into two ranges: 22–200 °C and 200-800 °C. A distinct behavior of strength was observed in each temperature range. At 200 °C, the compressive strength slightly increased by about 8%. With further increase in temperature the strength decreased and the loss of strength became more significant with temperature. The reduction in compressive strength was about 27% after exposure to 600 °C. At 800 °C, NS bricks lost most of their initial strength (~ 63%). Chang et al. (2006) showed that the compressive strength of concrete made with siliceous aggregate dropped by 35, 60 and 85% after heating at 400, 600 and 800 °C, respectively. Kulkarni et al. (2012) reported an increase

ACCEPTED MANUSCRIPT in the strength of siliceous aggregate concrete by 3% after heating at 300 °C, then a continuous reduction with temperature. At 450, 600, 750 and 900 °C, the compressive strength decreased by 23, 46, 60 and 80%, respectively. Similar trend was observed in heated WCS bricks except that in bricks containing 50%

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WCS there was a continuous increase in the strength up to 400 °C. The increase in compressive strength at 200 °C was 12% and 5.5% for 50% and 100% WCS bricks, respectively while the reduction at 800 °C was 22% and 39%. The strength loss in WCS bricks was lower than that in NS bricks. Moreover, although the unheated WCS bricks had the

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lowest compressive strength, the residual strengths of WCS bricks were higher than that of the NS bricks after exposure to 800 °C, indicating the resistance of WCS bricks to elevated

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temperatures. Similar findings were reported by Siddique and Kaur (2012) that the decrease in the compressive strength of concrete containing ground WCS exposed to elevated temperatures up to 350 °C is less than that in the concrete without WCS. On the other hand, solid cement bricks containing ACS as fine aggregate are very sensitive to elevated temperatures. It showed a continuous loss in strength even after heating

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to 200 °C and suffered severe losses in strength especially after exposure to 400 °C. The greater the content of ACS became, the greater the reduction in compressive strength tended to be. After exposure to 600 °C, the reduction in compressive strength in 50% ACS and 100% ACS was 29% and 42%, respectively. At 800 °C, most of ACS bricks were disintegrated. It

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should be noted that although ACS bricks were disintegrated more sharply than NS bricks after exposure to elevated temperatures, it had higher residual strength compared with NS

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bricks at temperatures up to 600 °C. Hence, ACS bricks exhibited a relatively lower thermal resistance than others.

Generally, the physical and mechanical properties of solid cement bricks changed with temperature as follows: Up to 200 °C, a small weight loss associated with an increase in the compressive strength was observed in all mixes (except ACS specimens) owing to the intensive departure of water in the form of steam leading to the hydration of unhydrated cement grains and formation of additional hydration products (Savva et al., 2005). From 400 °C, the physical and mechanical properties of the tested specimens decreased quickly. The specimens subjected to heating up to 600 °C had inferior properties, as represented by high

ACCEPTED MANUSCRIPT weight loss, strength loss and absorption percentage associated with the appearance of microcracks, indicating the destruction of binding forces by the dehydration of major cement hydrates such as Ca(OH)2 and C-S-H. Disintegration of coarse aggregate also occurred with heating as calcium carbonate decomposes between 700 and 900 °C and CO2 causing a

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destruction of the bricks (Chang et al., 2006; Fares et al., 2010; Heikal, 2000; Ruiz et al., 2005). Hence, the deterioration of solid cement bricks by exposure to elevated temperatures from 400 °C is due to: (1) the dehydration of cement hydrates, (2) the decomposition of aggregate, and (3) the thermal incompatibility between the behavior of aggregate and cement

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paste as cement paste first expands owing to its normal thermal expansion thereafter it shrinks as a result of loosing water by drying and dehydration of cement hydrates, while the aggregate

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undergoes progressive expansion with temperature. The two opposing actions progressively weaken and crack the bricks (Shoaib et al., 2001)

In general, the use of WCS as fine aggregate decreased the compressive strength of unheated bricks, while it increased the resistance of bricks exposed to elevated temperatures. The beneficial effect of WCS on the behavior of the heated bricks was confirmed by the

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results of the tests (i.e., strength loss, weight loss and absorption). This may be ascribed to the pozzolanic reaction of thermally activated WCS that consumes Ca(OH)2 to form additional CS-H with stronger binding forces and sufficient thermal stability during heating. Aguilar et al. (2010) noted that curing at 75 °C favored a contribution of the WCS sand to the compressive

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strength of geopolymeric concretes and the participation of WCS in the reactions depends strongly on the thermal activation. Furthermore, the honeycombed structure of WCS may

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reduce the thermal stresses in the bricks and reduce the likelihood of cracking. On the other hand, solid cement bricks containing ACS had inferior performance in elevated temperatures than NS and WCS bricks, irrespective of its high initial strength. This may be due to the higher fineness of ACS grains compared with NS or WCS grains (Fig. 2). The fine fractions in ACS densify the pore structure leading to a generation of high internal pressure by water vapors during heating and subsequently thermal cracking.

3.6 Relationship between compressive strength and heating temperature If a 2nd degree polynomial relationship is fitted to all data, correlation equations

ACCEPTED MANUSCRIPT expressing the relationship between the compressive strength of solid cement bricks and heating temperature will be established for each mix as follows:

, R2 = 0.9979

For NS bricks

(1)

Fc = -8E-06T2 - 0.0101T + 27.412

, R2 = 0.9322

For 50% ACS bricks

(2)

Fc = -9E-06T2 - 0.0193T + 32.665

, R2 = 0.953

For 100% ACS bricks

(3)

Fc = -4E-05T2 + 0.0261T + 18.11

, R2 = 0.9725

For 50% WCS bricks

(4)

Fc = -1E-05T2 - 6E-05T + 15.109

, R2 = 0.9576

For 100% WCS bricks

(4)

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Fc = -4E-05T2 + 0.0139T + 20.641

Where Fc is the compressive strength (MPa) and T is the heating temperature (°C). These

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equations are valid for solid cement bricks exposed to elevated temperatures up to 800 °C (except ACS bricks which can sustain elevated temperatures up to 600 °C only). There is a strong relationship between compressive strength and temperature, regardless of fine aggregate type. The suggested equations might be used for predicting the residual compressive strength of solid cement bricks made with different types of fine aggregates and

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exposed to elevated temperatures, such as in case of accidental fire or in some industrial applications, and hence tracing the residual load bearing capacity of the walls.

4. Conclusions

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This paper investigated the possibility of recycling BFS cooled by different techniques as alternative fine aggregate in the production of solid cement bricks with 200 kg/m3 cement

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content and coarse/fine aggregate ratio of 1.5. Such recycling of either ACS or WCS as fine aggregate in the production of solid cement bricks offers the following benefits: recycling of wastes causing environmental pollution, conservation of dumpsites, conservation of energy needed for grinding of slag before use, conservation of natural sand and consequently increasing cost saving, production of bricks with improved properties compared with traditional bricks and consequently increasing the lifetime of the structure and decreasing the overall cost for maintenance. Therefore, it is feasible from the environmental, technical and economical points of view to recycle BFS as fine aggregate in the production of solid cement bricks for sustainable development. However, cooling technique of BFS and replacement

ACCEPTED MANUSCRIPT percentage of NS should be taken into account as they have a remarkable effect on the behavior of the bricks at ambient and after exposure to elevated temperatures. The compressive strength and unit weight of the unheated bricks increased by using of ACS on contrary to the use of WCS. After exposure to elevated temperatures, NS and ACS

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bricks can sustain elevated temperatures up to 600 °C as load bearing units, while 50% WCS bricks can sustain elevated temperatures up to 800 °C as load bearing units. Although the heated ACS bricks suffered a greater decline in strength, larger absorption and disintegration more sharply than NS bricks, it had higher residual strength compared with NS bricks up to

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600 °C. So, a fire protection coating layer is recommended to be used on ACS bricks to insure the safety of the walls during any accidental fire. On the other hand, the use of WCS as fine

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aggregate is effective in minimizing the degradation of cement bricks after exposure to the elevated temperatures. WCS bricks demonstrated higher thermal stability than NS bricks. Solid cement bricks containing 50% WCS represent the most suitable fire resistant bricks up to 800 °C as it had sufficient properties after heating.

Based on the encouraging results obtained from this paper, it is recommended to use blast

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furnace slag either ACS or WCS to replace up to 100% of natural sand in the production of load-bearing solid cement bricks. Furthermore, WCS could be used as a fine aggregate in the production of thermally resistant bricks. It is also recommended to investigate the influence of using coarser ACS as fine aggregate on the behavior of solid cement bricks, especially after

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exposure to elevated temperatures.

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5. References

Aguilar, R., Díaz, O., García, J., 2010. Lightweight concretes of activated metakaolin-fly ash binders, with blast furnace slag aggregates. Constr. Build. Mater. 24, 1166-1175. Aldea, C., Young, F., Wang, K., Shah, S., 2000. Effects of curing conditions on properties of concrete using slag replacement. Cem. Concr. Res. 30, 465-472. ASTM C29/C29M-07, Standard Test Method for Bulk Density ("Unit Weight") and Voids in Aggregate, Annual Book of ASTM Standards, United States. ASTM C 67-03, Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile. Annual Book of ASTM Standards, United States.

ACCEPTED MANUSCRIPT ASTM C 90-03, Standard Specification for Loadbearing Concrete Masonry Units. Annual Book of ASTM Standards, United States. ASTM C117-04, Standard Test Method for Materials Finer than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing, Annual Book of ASTM Standards, United States.

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ASTM C128-07a, Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate, Annual Book of ASTM Standards, United States.

ASTM C 129-03, Standard Specification for Nonloadbearing Concrete Masonry Units, Annual Book of ASTM Standards, United States.

Annual Book of ASTM Standards, United States.

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ASTM C136-05, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates,

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Atiş, C., Bilim, C., 2007. Wet and dry cured compressive strength of concrete containing ground granulated blast-furnace slag. Build. Environ. 42, 3060-3065. Barnett, S., Soutsos, M., Millard, S., Bungey, J., 2006. Strength development of mortars containing ground granulated blast-furnace slag: effect of curing temperature and determination of apparent activation energies, Cem. Concr. Res. 36, 434-440.

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Berndt, M., 2009. Properties of sustainable concrete containing fly ash, slag and recycled concrete aggregate. Constr. Build. Mater. 23, 2606-2613. Cement Concrete and Aggregates, 2008. Australia, Use of recycled aggregates in construction, available at www.concrete.net.au/publications/pdf/RecycledAggregates.pdf

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Chang, Y., Chen, Y., Sheu, M., Yao, G., 2006. Residual stress–strain relationship for concrete after exposure to high temperatures. Cem. Concr. Res. 36, 1999-2005.

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Das, B., Prakash, S., Reddy, P., Misra, V., 2007. An overview of utilization of slag and sludge from steel industries. Resour. Conserv. Recycl. 50, 40-57. Demirboğa, R., Gül, R., 2006. Production of high strength concrete by use of industrial by-products. Build. Environ. 41, 1124-1127. Fares, H., Remond, S., Noumowe, A., Cousture, A., 2010. High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties. Cem. Concr. Res. 40, 488-496.

ACCEPTED MANUSCRIPT Galal, A., El-Didamony, H., Abo-El-Enein, S., Hussein, S., 2004. Durability of air- cooled slag cement pastes in seawater. International Conference: Future Vision and Challenges for Urban Development, Cairo, Egypt. Garcia, J., Perez, L., Gorokhovsky, A., Zamorano, L., 2009. Coarse blast furnace slag as a

an alkali activated cement. Constr. Build. Mater. 23, 2511-2517.

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cementitious material, comparative study as a partial replacement of portland cement and as

Heikal, M., 2000. Effect of temperature on the physico-mechanical and mineralogical properties of homra pozzolanic cement pastes. Cem. Concr. Res. 30, 1835-1839.

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Indian Minerals Yearbook (Part- II), 2012. Slag – iron and steel. 50th Edition, www.ibm.gov.in.

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Jariyathitipong, P., Hosotani, K., Fujii T., Ayano, T., 2013. Strength and durability of concrete with blast furnace slag. Third International Conference on Sustainable Construction Materials and Technologies, Kyoto, Japan.

Kalalagh, A., Marandi, S., Safapour, P., 2005. Technical effects of air cooled blast furnace slag on asphalt mixtures. J. Transp. Res. 2, 199-206.

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Khatib, J., Hibbert, J., 2005. Selected engineering properties of concrete incorporating slag and metakaolin. Constr. Build. Mater. 19, 460-472. Kulkarni, K., Yaragal, S., Narayan, K., 2012. Performance of high strength concrete subjected to elevated temperatures. International Journal of Earth Sciences and Engineering. 5, 593-598

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Laakri, M., Oudjit, M., Abdelli, K., 2014. Volumetric variation and rheology of cement based mineral additions (blast furnace slag and silica fume). Journal of Civil Engineering and

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Architecture. 8, 207-212.

Lau, A., Anson, M., 2006. Effect of high temperatures on high performance steel fibre reinforced concrete. Cem. Concr. Res. 36, 1698-1707. Nataraja, M., Kumar, P., Manu A., Sanjay, M., 2013. Use of granulated blast furnace slag as fine aggregate in cement mortar. Int. J. Struct. & Civil Eng. Res. 2, 59-68. Osborne, G., 1999. Durability of portland blast-furnace slag cement concrete. Cem. Concr. Compos. 21, 11-21. Oss, H., 2002. Slag-Iron and Steel. U.S. Geological Survey Minerals Yearbook. 701-706. Oss, H., 2013. Iron and steel slag, U.S. Geological Survey, Mineral Commodity Summaries.

ACCEPTED MANUSCRIPT 82-83. Ruiz, L., Platret, G., Massieu, E., Ehrlacher, A., 2005. The use of thermal analysis in assessing the effect of temperature on a cement paste. Cem. Concr. Res. 35, 609-613. Saad, M., Abo-El-Eneini, S., Hanna, G., Kotkatat, M., 1996. Effect of temperature on

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physical and mechanical properties of concrete containing silica fume. Cem. Concr. Res, 26, 669-675.

Sadek, D., El-Attar, M., 2012. Development of high-performance green concrete using demolition and industrial wastes for sustainable construction. Journal of American Science. 8.

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http://www.americanscience.org.

Savva, A., Manita, P., Sideris, K., 2005. Influence of elevated temperatures on the mechanical

Cem. Concr. Compos. 27, 239-248.

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properties of blended cement concretes prepared with limestone and siliceous aggregates.

Shi, C., Qian, J., 2000. High performance cementing materials from industrial slags - A review. Resour. Conserv. Recycl. 29, 195-207.

Shoaib, M., Ahmed, S., Balaha, M., 2001. Effect of fire and cooling mode on the properties of

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slag mortars. Cem. Concr. Res. 31, 1533-1538.

Siddique, R., Kaur, D., 2012. Properties of concrete containing ground granulated blast furnace slag (GGBFS) at elevated temperatures. J. Adv. Res. 3, 45-51. Slag Cement Association, Slag Cement in Concrete - Terminology and Specifications, 2003.

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The Japan Iron and Steel Federation- Nippon Slag Association, The Slag Sector in the Steel Industry, Japan, 2006.

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Yeau, K., Kim, E., 2005. An experimental study on corrosion resistance of concrete with ground granulate blast-furnace slag. Cem. Concr. Res. 35, 1391-1399. Yüksel, I., Genç, A., 2007. Properties of concrete containing nonground ash and slag as fine aggregate. ACI Mater. J. July-August, 397-403. Zeghichi, L., 2006. The effect of replacement of naturals aggregates by slag products on the strength of concrete. Asian Journal of Civil Engineering. 7, 27-35. Zhang, B., Bicanic, N., Pearce, C., Phillips, D., 2002. Relationship between brittleness and moisture loss of concrete exposed to high temperatures. Cem. Concr. Res. 32, 363-371.

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NS 2.5 1.65 0.3

ACS 2.55 1.79 10.2

WCS 2.46 1.5 0

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Table 2 Physical properties of fine aggregates. Property Specific gravity (SSD) Unit weight (t/m3) Clay and fine materials (%)

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Table 1 Chemical composition of BFS. Component SiO2 Al2O3 Fe2O3 CaO MgO K2O SO3 Na2O MnO L.O.I % 37.3 13.1 0.76 29.8 5.5 1.14 2.32 1.33 4.0 0.02

Fine aggregate Sand ACS 792 ‫ــــ‬ 396 396 ‫ــــ‬ 792 ‫ــــ‬ 396 ‫ــــ‬ ‫ــــ‬

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Table 3 Mix proportions for solid cement bricks (kg/m3). Mix % Coarse Series Cement No. Sand ACS WCS aggregate Control 1 100 0 0 200 1188 2 50 50 0 200 1188 I 3 0 100 0 200 1188 4 50 0 50 200 1188 II 5 0 0 100 200 1188

WCS ‫ــــ‬ ‫ــــ‬ ‫ــــ‬ 396 792

Water 174 179 187 188 202

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Fig. 1. XRD patterns of BFS at room temperatures: (a) ACS and (b) WCS

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Fig. 2. Grading of fine aggregates.

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Fig. 3. The appearance of the bricks just after pressing.

100% ACS specimen

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100% WCS specimen

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Fig. 4. Specimens' surface after heating to 800 ° C and cooling.

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Temperature (°C)

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Fig. 5. The effect of temperature on the unit weight of solid cement bricks.

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Contol mix 100%ACS

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Fig. 6. Weight loss of solid cement bricks: (a) ACS series and (b) WCS series.

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Absorption (kg/m3)

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Fig. 7. The effect of temperature on the absorption of solid cement bricks.

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Fig. 8. The effect of temperature on the compressive strength of solid cement bricks (a) ACS series and (b) WCS series.

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Limit for load bearing units from ASTM C 90-03, 2005, and limit for non-load bearing unit from ASTM C 129-03

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Journal of Cleaner Production

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Highlight Manuscript Title : Effect of Cooling Technique of Blast Furnace Slag on the Thermal Behavior of Solid Cement Bricks

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It is feasible to recycle BFS without processing in bricks for sustainability. Cooling technique of BFS has a remarkable effect on the behavior of the bricks. WCS bricks are thermally more stable than NS and ACS bricks. WCS could be used as fine aggregate in manufacturing of thermally resistant bricks.

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