Compressive strength behavior of concrete by partial replacement of regular brick with over-burnt brick aggregate

Transcription

1 Innov. Infrastruct. Solut. (217) 2:11 DOI 1.17/s TECHNICAL NOTE Compressive strength behavior of concrete by partial replacement of regular brick with over-burnt brick aggregate Md. Robiul Awall 1 Md. Oli-Ur-Rahaman 1 Md. Samdani Azad 1 Shaikh Fazle Rabbi 1 Received: 24 January 217 / Accepted: 17 April 217 / Published online: 25 April 217 Ó Springer International Publishing Switzerland 217 Abstract Numerous kinds of coarse aggregates are being used around the world, and most of these coarse aggregates are naturally originated. Due to the gradual diminution of natural resources, modern society is facing a challenge in concrete work which demands a huge amount of coarse aggregate. In Bangladesh, handful brick fields around the country made brick aggregate available as well as economical compared to natural coarse aggregates. Uncontrolled heat in brick kilns produces a good number of overburnt bricks. Due to the unevenness, those bricks are staked as an idle in brick fields. Those over-burnt brick could be a source of recycled coarse aggregate. This paper highlights on the behavior of concrete, prepared by the partial replacement of regular brick aggregate (RBA) with overburnt brick aggregate (OBBA) in a range from to 1%. Three different water cement ratios (.5,.55 and.6) are considered in this study. Result shows that compressive strength of concrete increases with the increment of OBBA content. For 75% replacement of RBA with OBBA in concrete increases the compressive strength by 33%. Unit weight of concrete decreases with the increment of OBBA content. The lowest achieved unit weight of concrete is 79% of the usual value of unit weight of concrete. The slump test was conducted for each batches of mixing, and & Md. Robiul Awall robi95@gmail.com Md. Oli-Ur-Rahaman oli1164@gmail.com Md. Samdani Azad samdani.civil.ruet@gmail.com Shaikh Fazle Rabbi rabbyruet@yahoo.com 1 Civil Engineering Department, RUET, Rajshahi, Bangladesh the slump values are in between the range of cm. OBBA in concrete could decrease structure s dead load and increase its strength with a provision of economy. Keywords Brick aggregate Over-burnt bricks Concrete Compressive strength Introduction Necessity of the locally manufactured building materials is highly being over-emphasized in many places in Bangladesh because there is a discrepancy between the demands for concrete works and expensive conventional construction materials coupled with the depletion of traditional building materials including the natural coarse aggregates. Estimated 5 brick kilns operate across Bangladesh with an annual production of 17.2 billion bricks including approximately 1 surrounding Dhaka, the capital city of Bangladesh which makes the brick aggregate available and economical compared to the other customary coarse aggregates [1]. Besides, many researches showed the fact that brick aggregate could be a better alternative to the usual aggregates. Rashid et al. [2] found that higher strength concrete (f cu = N/mm 2 ) with brick aggregate is achievable. Cachim [3] reported that natural aggregate could be replaced by 15% of brick aggregate without affecting the strength. According to Sable and Walke [4], up to 3% brick aggregate replacement for natural coarse aggregate is found feasible and economical. Aguwa [5] studied the properties of brick aggregate concrete and reported the concrete as lightweight concrete. In the clay brick production by burning clay soil in Bangladesh, a good number (approximately 13%) are severely over-burnt due to the uncontrolled and uneven distribution

2 11 Page 2 of 7 Innov. Infrastruct. Solut. (217) 2:11 of temperature in the kiln. Properly burnt bricks are treated ideal for construction work either in partition wall or as coarse aggregate in concrete, whereas the over-burnt bricks are usually considered as useless and are not allowed in construction works. Many researchers have been accomplished to investigate the suitability of OBBA in concrete. The studies show that higher strength concrete is achievable by replacing stone or gravel aggregates by OBBA. Patil and Autade [6] investigated the performance of concrete for replacement of stone aggregate with OBBA (jhama class brick aggregate) and found that the compressive strength was 11.95% higher than that of conventional concrete for the replacement 4%. Tariq et al. [7] conducted a study on concrete for the partial replacement of gravel aggregate with OBBA within a range of 2%. The study found strength of MPa after 28-day curing for 2% replacement of gravel. Suitability of crushed overburnt brick aggregate was investigated by Apebo et al. [8]. The study found that the concrete contains OBBA as coarse aggregate shows a compressive strength of 29.5 MPa at.4 w/c ratio whereas for gravel stone concrete shows a maximum value of 3.8 MPa at same w/c ratio. Kulkarmi and Momin [9] investigated the properties of concrete composed of OBBA as coarse aggregate and found a maximum strength of MPa at w/c ratio.55 for the mixing ratio 1:1.5:2. Another different research was conducted by Apebo et al. [1] to study the compressive strength of concrete with partial replacement of gravel aggregate with OBBA in three different w/c ratios. The study shows the compressive strength decreases with the increment of w/c ratios. Apebo et al. [11] conducted another study to obtain the relationship between the percentage of OBBA content and compressive strength of concrete. The study found a sudden increment of strength at 25% OBBA content but at 5% OBBA content the strength decreases and beyond that content the strength of concrete increases and gains a maximum value of 26 MPa at 1% replacement of gravel with OBBA. Another important criterion of concrete is workability which is measured by the slump value of concrete. Various researches showed that OBBA content affects the slump value of concrete. Tariq et al. [12] showed that slump value decreases from to 19.5 mm with the increment of OBBA from to 2%. Apebo et al. [11] investigated the slump value of the concrete within wide variety of percentage replacement of gravel coarse aggregate by OBBA and fund an increment of slump value at 25% of OBBA and after that the slump value decreases with the increment of OBBA in concrete. The research shows that the unit weight of concrete decreases with the increment of OBBA in concrete. Tariq et al. [12] found 7.8% reduction in unit weight of concrete. Kulkarmiand Momin [9] showed the unit weight of RBA concrete and OBBA concrete is in the range of 1 12 kg/m 3 ; hence, brick aggregates can be considered as lightweight aggregates concrete. Almost all the previous studies discussed above are conducted by the partial replacement of gravel or stone aggregate with OBBA. Those studies indicate that natural aggregates could be partially replaced by OBBA with a satisfactory result in compressive strength, unit weight and workability. In present study, the performance of concrete is investigated by the partial replacement of RBA with OBBA because RBA is adequately available compared to any other natural coarse aggregates in Bangladesh. Materials All the materials used in this study are available in Bangladesh. Fine aggregate, locally known as Domar Sand is a river washed and collected from Sylhet district. RBA and OBBA are collected from brick field in Rajshahi district. The ordinary Portland cement (OPC) type CEM-II is collected from a renowned cement company of Bangladesh. Figure 1 shows the materials used in this study. Specific gravity tests for coarse aggregate (CA) and fine aggregate (FA) were conducted according to ASTM C 127 [13] and ASTM C 128 [14]. Dry rodded unit weight of CA was determined according to ASTM C 29 [15]. The water Table 1 Water absorption, specific gravity and unit weight Properties FA RBA OBBA Specific gravity Absorption (%) Unit weight (kg/m 3 ) Fig. 1 Materials used in the study: a fine aggregate; b regular first-class brick aggregate; and c over-burnt brick aggregate

3 Innov. Infrastruct. Solut. (217) 2:11 Page 3 of 7 11 Parcentage finer (%) Parcentage finer (%) Particle size (mm) (a) Particle size (mm) (c) Particle size (mm) Fig. 2 Grain size distribution curve for aggregates: a fine aggregate; b regular first-class brick aggregate; and c over-burnt brick aggregate Table 2 Engineering properties of OPC absorption, specific gravity, unit weight of CA and FA are shown in Table 1. Dry sieve analyses of FA and CA were conducted according to ASTM C 136 [16], and the grain size distribution curves are shown in Fig. 2. The setting time of Parcentage finer (%) Properties (b) Values Initial setting time 116 min Final setting time 344 min Specific gravity 3.1 ordinary Portland cement (OPC) used in this study was determined according to ASTM C 191 [17]. Table 2 shows the basic properties of the OPC. Methodology This research was destined to study the behavior of concrete with a variation of percentage of OBBA in concrete replacing RBA with an interval of 25% in different w/c ratios. The percentages of OBBA in composition of concrete specimen were, 25, 5, 75 and 1% of total CA. The water cement ratios were.5,.55 and.6. For each individual composition, three specimens and in-total 45 concrete specimen cylinders of 1 ft. height and 6 in. diameter were molded. Concrete mix design was conducted according to the ACI Absolute Volume Method for a desired strength of 2 MPa, and a standard deviation of the strength was considered as 4 MPa. The ratios found from the mix design were 1:2:4 for the desired strength. Before mixing, the materials were batched by weight. FA was sieved to get rid of foreign matters. Water absorption of RBA is high. So, the RBA was soaked for 24 h before batching and mixing. Saturated surface dry (SSD) conditions of the coarse aggregates were ensured before the concrete mix preparation. Concrete mix was prepared by hand mixing. Slump test was conducted after finishing the mixing of each batch according to ASTM C 143 [18]. The concrete specimens were prepared by filling the molds in Fig. 3 Experimental setup for tests: a slump test; b unit weight determination; and c compressive strength test

4 11 Page 4 of 7 Innov. Infrastruct. Solut. (217) 2:11 Table 3 Slump values for corresponding OBBA content and w/c ratios w/c ratios Percentage of OBBA in concrete (cm) % 25% 5% 75% 1% Table 4 Unit weight of concrete OBBA (%) Unit weight of concrete (kg/m 3 ) five layers gradually and 25 blows per layer with a standard temping rod. For the mixing and placing of fresh concrete, ASTM C 192 [19] has been followed. The casted molds were kept for 12 h for proper setting. After 12 h, concrete specimens were demolded and immersed in the potable water for the curing of 28 days. After the curing, the concrete cylinders were brought out from the water and kept in the air for 6 h. Then, their weights were taken. After that, compressive strength test of the concrete cylinders was conducted in a universal testing machine (UTM) according to ASTM C 39 [2]. Experimental setups are shown in Fig. 3. Results and discussion Slump test result Workability is property of fresh concrete which determines the ease and homogeneity with which it can be mixed, placed, compacted and finished. Slump test is a measurement of workability of concrete. Table 3 shows the slump value obtained for different mixes. Figure 4a shows the variation of slump values with respect to the percentage of OBBA. For w/c ratio.55 and.6, the slump values are decreasing with the increment of the OBBA content up to 5% of OBBA content. But after 5% of OBBA, the slump values are increasing with the increment of OBBA content up to 1% of OBBA content. For w/c ratio.5, the slump value is increasing at 25% of OBBA content but decreases at 5% of OBBA content and then further increases with the increment of OBBA content. The slum value of the fresh concrete depends largely on the porosity and the surface area of RBA and OBBA. Figure 4b shows the variation of slump values with respect to the three w/c ratios. Generally, slump value of concrete increases with the increment of w/c ratios. The concrete mix which contains, 25 and 1% OBBA states that phenomenon. But the mixes containing OBBA of 5% and 75% show different aspects. In those cases, slump values increase for w/c ratios.5.55 and the values decrease for w/c ratios Fresh concrete is a mixture of granular materials (CA, FA and OPC) with water. The mixing water imparts fluidity to the mixture and makes the mixture viscoplastic. In rheological point of view, slump test is nothing but the deformation of fresh concrete subjected to its own weight. In present study, the slump value of the fresh concrete depends largely upon the cohesiveness of the mortar with aggregates and the unit weight of CA. The fresh concrete contains RBA greater than 5%, which shows an improved cohesion with mortar because RBA has larger contact area compared to OBBA. On the other hand, the unit weight of OBBA is lesser than RBA. Thus, when OBBA content increases, the weight of the fresh concrete decreases. The lesser the load, lesser the deformation. For this reason, the slump value of fresh concrete decreases within the range of OBBA content from to 5%. Fig. 4 Variation of slump values with respect to: a percentages of OBBA; b w/c ratios (a) Slump Value (cm) w/c ratio.5 2 w/c ratio.55 w/c ratio OBBA (%) Slump Value (cm) O% OBBA 25% OBBA 2 5% OBBA 75% OBBA 1% OBBA w/c ratio Variation of slump value with percentages of OBBA Variation of slump values with w/c ratios (b)

5 Innov. Infrastruct. Solut. (217) 2:11 Page 5 of 7 11 Density of concrete (kg/m 3 ) y = x R² = OBBA (%) Fig. 5 Variation of unit weight with respect to percentage of OBBA in concrete Table 5 Compressive strength of concrete for corresponding OBBA content and w/c ratios w/c ratios Percentage of OBBA in concrete (MPa) % 25% 5% 75% 1% Again, slump value of fresh concrete increases within the range from 5 to 1% of OBBA content. When OBBA content increases in the concrete, cohesion between the mortar and aggregate decreases because OBBA has lesser contact area than RBA. For this reason, though the weight of the fresh concrete decreases, the slump value increases with the increment of OBBA content within this range. Unit weight of concrete Unit weight of concrete is another important property of concrete. The present concern about lightweight concrete is overstated for need of earthquake resistance structures. The unit weight of OBBA is kg/m 3 which is 6.5% greater than the ASTM specified bulk density of lightweight aggregate. According to the ASTM C 33 [21], the maximum dry loose bulk density of lightweight aggregate is 88 kg/m 3. The unit weight of concrete made of regular aggregates (gravel or stone aggregate) is 24 kg/m 3. Table 4 shows the unit weight of the concrete specimens for corresponding OBBA content. Figure 5 shows the variation of the density with the increment of OBBA content. The unit weight of concrete decreases with the increment of OBBA content in concrete. The variation is almost linear. Compressive strength test result The compressive strength of concrete is tabulated in Table 5 with corresponding w/c ratios and percentage of OBBA. Figure 6a represents the variation of compressive strength with respect to the OBBA content of concrete. The compressive strength increases at 25% OBBA content but decreases at 5% OBBA content and further the compressive strength increases with the increment of OBBA content. The reason of the slight depletion of strength at 5% OBBA content is the presence of two different types of aggregate in equal amount which affects the bonding between two different types of aggregate. Again, other factors like strength of single aggregate, porosity of aggregate could be the reasons behind the depletion of strength at 5% of OBBA content. Strength (MPa) (a) w/c ratio.5 w/c ratio.55 w/c ratio OBBA (%) Variation of compressive strength with percentages of OBBA Strength (MPa) w/c ratio (b) % OBBA 25% OBBA 5% OBBA 75% OBBA 1% OBBA Variation of compressive strength with w/c ratios Fig. 6 Variation of compressive strength with respect to: a percentages of OBBA; b w/c ratios

6 11 Page 6 of 7 Innov. Infrastruct. Solut. (217) 2:11 Figure 6b represents the variation of compressive strength with respect to the w/c ratios. The compressive strength of concrete decreases with the increment of the w/c ratios. But the variation patterns are not the same. For and 1% OBBA content, the strength decreases slightly within the w/c ratios.5.55, but the reduction in strength is more rapid at the range For 5 and 75% OBBA content, the strength decreases rapidly within the w/c ratios.5.55, but within the range of.55.6 the strength reduces slowly. For 25% OBBA content, the strength reduces almost linearly trough the range of the w/c ratios.5.6. Conclusion Investigations have been made to study the behavior of concrete which includes the compressive strength, unit weight of hardened concrete and slump value of fresh concrete. The variable parameters of the study were the percentage replacement of RBA with OBBA and the w/c ratios. Within the scope of this study, it can be conclude that 1. Compressive strength of concrete influenced largely by the mortar aggregate interlocking mechanism. Due to the porosity, OBBA shows an improved interlocking with mortar which affects the result of compressive strength. The compressive strength of concrete increases at 25 and 75% of OBBA content but decreases at 5% OBBA content. Another influencing parameter is w/c ratio. Strength of concrete decreases with the increment of w/c ratios. In present study, maximum strength of MPa was obtained at w/c ratio.5 for 75% OBBA content. 2. Various parameters affect the slump value of fresh concrete, but in present study, unit weight of the aggregates and the contact area of the aggregates are dominant of all. Unit weight of OBBA is smaller than RBA. Again, RBA poses larger contact area compared to OBBA. Due to these facts, the weight of fresh concrete and the total aggregate mortar contact area varies with change of OBBA content. The slump values decrease with the increment of OBBA content up to 5%. Beyond that percentage, slump value increases with the increment of OBBA content in the concrete. The slump value for batch of fresh concrete was within the range from 3.5 to 1 cm. 3. Unit weight of concrete depends upon the unit weight of aggregates. Unit weight of concrete decreases with the increment of OBBA content because the unit weight of OBBA is lesser than RBA. The relationship between the unit weight of concrete and the percentage of OBBA content is almost linear. The maximum reduction in unit weight is 7% compared to the concrete specimen which contains 1% RBA. In general, the unit weight of concrete is 24 kg/m 3. The unit weight of concrete specimen contains 1% OBBA is 1895 kg/m 3 which is 79% of the ideal value. References 1. The world bank (211) Introducing Energy-efficient clean technology in the brick sector of Bangladesh. The world bank, Washington DC, USA. 2. 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7 Innov. Infrastruct. Solut. (217) 2:11 Page 7 of ASTM C 143 (23) Standard test method for slump of hydraulic-cement concrete. Annual Book of ASTM Standard, 19. ASTM C 192 (22) Standard practice for making and curing concrete test specimens in the laboratory. Annual Book of ASTM Standard, 2. ASTM C 39 (214) Standard test method for compressive strength of cylindrical concrete specimens. Annual Book of ASTM Standard, 21. ASTM C 33 (24) Standard specification for lightweight aggregates for structural concrete. Annual Book of ASTM Standard,