Properties of higher strength concrete made with crushed brick as coarse aggregate

Transcription

1 Journal o Civil Engineering (IEB), 37(1) (2009) Properties o higher strength onrete made with rushed brik as oarse aggregate Mohammad Abdur Rashid a, Tanvir Hossain a, and M. Ariul Islam b a Department o Civil Engineering Dhaka University o Engineering and Tehnology, Gazipur 1700, Bangladesh b Civil Tehnology, Sai Institute o Management and Tehnology, Mirpur, Dhaka, Bangladesh Reeived on 14 June 2008 Abstrat An investigation was ondued to ahieve onrete o higher strength using rushed brik as aggregate and study the mehanial properties. It was ound that higher strength onrete ( = 4500 to 6600 psi 1 ) with brik aggregate is ahievable whose strength is muh higher than the parent unrushed brik. Test results show that the ompressive strength o brik aggregate onrete an be inreased by dereasing its water-ement ratio and using admixture whenever neessary or workability. The ompressive strength as well as the tensile strength and the modulus o elastiity o the onrete were studied. The ylinder strength is ound about 90% o the ube strength. The ACI Code relations or determining the modulus o rupture was ound to highly underestimate the test values., whereas the ode suggested expression or elasti modulus gives muh higher values than the experimental ones or brik aggregate onrete. Relations were proposed to estimate the modulus o rupture and the modulus o elastiity o brik aggregate onrete o higher strengths Institution o Engineers, Bangladesh. All rights reserved. Keywords: Brik aggregate, onrete, ylinder and ube strengths, elastiity, water-ement ratio. 1. Introdution In Bangladesh and parts o West Bengal, India, where natural rok deposits are sare, burnt lay briks are used as an alternative soure o oarse aggregate. In Bangladesh the use and perormane o onrete made with broken brik as oarse aggregate are quite extensive and satisatory. Clay an be burnt in its natural orm as is done in brikmaking and the produt may be a soure o oarse aggregate or onrete. Also in brikmaking, a large number o briks are rejeted due to nononormity with the required speiiations. One suh major nononormity is the distorted orm o brik produed 1 1 MPa = psi

2 44 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) due to the uneven temperature ontrol in the kiln. These rejeted briks an also be a potential soure o oarse aggregate. This would not only make good use o the otherwise waste material but would also help alleviate disposal problems. In spite o extensive use o brik aggregate onrete in this regions and the apparent satisatory perormane o the strutures already built, no systemati investigation was onduted and properly doumented. The urrent designs or brik aggregate onretes are based on intuition and aumulation o experiene, rather than on sound experimental evidene. The pratial experienes onidently showed us that the maximum range o ompressive strength o onretes made with brik aggregate but without using any admixture is around 3000 psi. However, higher strength onrete ( muh greater than 3000 psi) an be used advantageously in ompression members suh as olumns and piles. In olumns, the redution in size will lead to redued dead load and subsequently to redued total load on the oundation system. Smaller olumn size also means more available loor spae to use. The relatively higher ompressive strength per unit volume will also signiiantly redue the dead load o lexural members. In addition, higher strength onrete possessing a highly dense mirostruture is likely to enhane long-term durability o the struture. The mix proportion o the onrete is usually done either by the ACI method (1994) or the BS method (1985). In both methods, the oarse aggregate is the rushed natural stones and the unit weight o this onrete ranges rom 140 to 152 pounds per ubi oot (p 2 ) (Nilson and Darwin, 1997), whereas brik aggregate onrete weighing between p an be termed as medium weight onrete in omparison with normal weight and light weight onrete (Akhteruzzaman and Hasnat 1983). Besides, the texture and surae roughness o brik aggregates are dierent rom those o stone aggregate. So the properties o brik aggregate onrete may not ollow exatly the same trends as those o stone aggregate onrete. Consequently, the present odal speiiations, whih are based on stone aggregate onrete may not be appliable or brik aggregate onrete. Some studies are ound in the literature. Akhtaruzzaman and Hasnat (1983) investigated the various engineering properties o onrete using rushed brik as oarse aggregate. Khaloo (1994) studied the properties o onrete using rushed linker brik as oarse aggregate. In both the above-mentioned studies, investigations were also done by omparing the properties o brik aggregate onrete with those or stone aggregate onrete. On the other hand, studies were done by Mansur et al. (1999) omparing the properties o stone aggregate onrete with those o equivalent brik aggregate onrete obtained by replaing stone with an equal volume o rushed brik, everything else remaining the same. The present study reports primarily at to ahieve higher strength onrete using rushed brik as oarse aggregate. Various mehanial properties o brik aggregate onrete are also studied and ompared with those determined ollowing the odal speiiations or stone aggregate onrete. 2. Experimental investigation In this study, manually rushed well burnt (gas burnt) lay briks were used as ¾ in. ( p = kg/m 3

3 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) mm) down-graded oarse aggregate. The briks used were well shaped and reddish in olor. The average ompressive strength o the briks was psi (30.9 MPa). A mixture o oarse sand (Sylhet sand) and loally available ine sand in the ratio o 1:1 was used as ine aggregate. The ineness modulus o the mixed sand and the brik aggregate were 1.86 and 6.97 respetively and their absorption apaities were 2.6% and 15.8% respetively. The physial properties o brik aggregate and sand are given in Table 1. Type-I ordinary Portland ement was used in all ases. In the experimental program, our basi mixes designated by A, B, C, and D were hosen to attain target strengths (28 day ylinder ompressive strength) o 4500, 5000, 5500, and 6000 psi respetively. The orresponding mix ratios were seleted ollowing the ACI speiiations (1994) or onrete mix design. The details o the various mixes are presented in Table 2. Table 1 Properties o aggregates used Type o aggregate Bulk speii Dry rodded unit Absorption Fineness gravity (SSD*) weight (lb/t 3 ) apaity ( % ) modulus Coarse Aggregate Fine Aggregate *Saturated surae dry Table 2 Details o onrete mix proportions Mix Target ylinder strength (psi) Mix ratio by weight (ement : sand : brik aggregate) w/ ratio by weight % o admixture by weight o ement A : 1.50 : B : 1.30 : C : 1.20 : D : 1.06 : Casting o speimens The graded aggregates (both ine and oarse aggregates) were soaked in water or 24 hours and then air-dried to saturated surae dry (SSD) ondition beore mixing with other ingredients. To improve the workability o the two mixes: C and D, a superplastiizer SIKAMENT-280(M) [modiied melamine and naphthalene ormaldehyde sulphonate type] was added in the proportions as mentioned in Table 2. For eah mix, all o the ingredients with appropriate proportions were added in the mixture mahine, then mixing was done or about 2 minutes. The workability o the resh onrete was measured with a standard slump one immediately ater mixing. A slump o 1" to 2" was measured or onretes without an admixture, whereas the slump value or onretes with admixture was reorded rom 3" to 4". The test speimens were ast in steel molds and ompated with a vibrator nozzle. They were demolded 24 hours ater asting and were ured under water until 24 hours beore the test. Eah o the mixes omprised o ive ylinders, our 6 -ubes and three prisms Testing o speimens For eah mix o onrete, three ylinders and our 6 -ubes were tested to

4 46 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) determine the ompressive strengths. The remaining two 12 -ylinders were tested to determine the modulus o elastiity. Whereas three prisms were tested under single point loading to determine the modulus o rupture. A 1000-kN apaity universal testing mahine was used to test all o the above mentioned speimens. Typial ailure patterns o ylinder and ube are shown in Fig Test results and disussions Test results are presented in igures and tables and disussed ategorially. The results inlude ylinder ompressive strength, ube ompressive strength u, modulus o rupture r, and modulus o elastiity E. The means o the test values or eah o the properties are presented in Table 3. In this table, the ratios o the atual to the targeted ylinder strengths indiate that the desired onrete strengths have suessully been ahieved in this study. The ratios o the values o various properties o onrete with the orresponding ompressive strength values (either or, ) are presented in Table 4. Table 3 Various properties o onretes Mix Target ylinder omp. strength (psi), tgt Atual ompressive strength (psi) Cylinder, Cube, u Tensile strength (psi) r Modulus o elastiity E (psi) Ratio, tgt A B C D * Mean 1.02 SD** *The test speimens ould not be ailed due to the limitation o the apaity o testing mahine ** Standard deviation Table 4 Relations between the various properties o onretes Cylinder strength Ratio Ratio Ratio Ratio Mix r E (psi) r u A B C D Mean SD* *Standard deviation

5 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) (a) Cylinder (b) Cube Fig. 1. Typial ailure patterns o ylinder and ube speimens 3.1 Eet o water-ement ratio on ompressive strength The eet o water-ement (w/) ratio on the ompressive strength o onrete measured at 28-days on standard ylinder is shown in Fig 2. From this igure it is seen that onrete strength is redued drastially with the inrease o w/ ratio. Also the rate o redution o onrete ompressive strength appears to be higher or lower w/ ratio. A regression analysis shows the ollowing relationship between the onrete ompressive strength and the w/ ratio (Fig. 2). 2 w w (1) in whih the strength value is in pound per square inh (psi) and the w/ ratio is by weight.

6 48 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) Cylinder strength, ' (psi) ' = 73517(w/) (w/) R 2 = water-ement (w/) ratio, (by weight) Fig. 2. Variation o onrete ompressive strength with the variation o w/ ratio 3.2 Relationship between ylinder and ube ompressive strengths Figure 3 shows the relationship between the ratio o ylinder to ube ompressive strengths with the ube ompressive strength. Generally or normal weight and normal strength onretes the ylinder ompressive strength is approximately 0.80 o the ube ompressive strength (Neville and Brooks 2002). However rom Table 4 it is seen that the mean o ylinder to ube ompressive strengths is 0.91 with a standard deviation (SD) o or the onrete strength-range studied. It an be seen rom Fig. 3 that higher the ompressive strength, the higher is the value o the ratio o ylinder to ube ompressive strengths. Akhtaruzzaman and Hasnat (1983) and Mansur et al. (1999) also reported similar indings. A linear regression analysis shows the ollowing relationship between the ratio o ylinder to ube ompressive strengths and the ube ompressive strength (Fig. 3) u u (2) in whih all strength values are in psi.

7 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) Ratio ( ' / u) ( ' / u ) = 3 x 10-5 ( u ) R 2 = Cube strength, u (psi) Fig. 3. Relation between ylinder and ube ompressive strengths 3.3 Relationship between tensile and ompressive strengths Using the test data, a relationship between the modulus o rupture and the ylinder ompressive strength is presented in Fig 4. As expeted, the tensile strength ( r ) inreases with inrease in ompressive strength ( ) o onrete. Akhtaruzzaman and Hasnat (1983) and Mansur et al. (1999) also reported similar trends. The more angular shape and rougher surae texture o brik aggregate possibly enhaned the interaial bond, thus resulting in a higher tensile strength. It an also be seen that the modulus o rupture inreases linearly with the inrease in ompressive strength. The ACI Code (1999) proposed relation ( r 7. 5 ) or normal weight onrete is also plotted to make a omparison (Fig. 4). However, the ACI ode expression underestimates (about 40%) the values o modulus o rupture o brik aggregate onrete (Fig. 4 and Table 4). From Table 4, it an be seen that the mean o the ratios o modulus o rupture to ylinder ompressive strength is 0.18 with a SD o A linear regression analysis shows the ollowing relationship between the modulus o rupture and the square-root o ylinder ompressive strength (Fig. 4 and Table 4) r in whih all strength values are in psi. (3)

8 50 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) Modulus o rupture, r (psi) Proposed: r = 12.8 ( ' ) 0.5 ACI relation: r = 7.5 ( ' ) Cylinder strength, ' (psi) Fig. 4. Relation between modulus o rupture and ompressive strength 3.4 Relationship between modulus o elastiity and ompressive strength Fig. 5 shows the plot o the seant modulus o elastiity against the orresponding ylinder strength. As expeted, an inrease in onrete strength inreases the elasti modulus o brik aggregate onrete. For omparison purpose, the ACI Code (1999) 1.5 suggested relationship E 33 w is also plotted in the same igure. The unit 130 w weight o brik aggregate onrete p has been onsidered in this relation. From the Fig. 5 and Table 4, it is obvious that the ACI Code (1999) relationship overestimates (about 30%) the elasti modulus o brik aggregate onrete. For the unit weights o brik aggregate onrete used in this study and the range o ylinder strength tested, the elasti modulus ( ) an be expressed empirially by E E in whih both strength and elasti modulus are in psi. 4. Conlusions The ollowing onlusions may be drawn rom the present study: (1) Crushed briks may be used satisatorily as oarse aggregate or making onrete, the strength o whih is muh higher than that o briks onsidered. The unit weight o suh onrete is around 130 pounds per u t whih is about 13% lower than that o normal weight onrete. (2) Similar to normal weight onrete a drasti redution in the ompressive strength o brik aggregate onrete due to the inrease in water-ement ratio has been ound. The rate o this strength redution is higher or lower water-ement ratio. (3) The ylinder ompressive strength has been ound about 90% o the orresponding (4)

9 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) ube ompressive strength or brik aggregate onretes studied. The higher the ompressive strength the higher is the ratio o ylinder to ube ompressive strengths. Eq.(2) may be used to orrelate ylinder and ube ompressive strengths o brik aggregate onrete. 5.0E E+06 Elasti modulus, E (psi) 4.0E E E E E+06 ACI relation: E = 33(w ) 1.5 ( ' ) 0.5 Proposed: E = ( ' ) E Cylinder strength, ' (psi) Fig. 5. Relation between onrete ompressive strength and modulus o elastiity (4) The ACI Code (1999) expression underestimates (about 40%) the values o modulus o rupture or brik aggregate onrete. The Eq. (3) may be used to estimate the modulus o rupture o brik aggregate onrete. (5) The ACI Code (1999) expression overestimates (about 30%) the values o modulus o elastiity or brik aggregate onrete. The Eq. (4) may be used to estimate the elasti modulus o higher strength brik aggregate onrete. Aknowledgment The experimental work desribed was exeuted at the Department o Civil Engineering, Dhaka university o Engineering and Tehnology, Gazipur 1700, Bangladesh, whose support is greatly appreiated. Reerenes ACI 318R-99 (1999), Building ode requirements or reinored onrete and ommentary, ACI Committee 318, Amerian Conrete Institute, Farmington Hills, Mihigan, pp.391. ACI Committee (1994), Standard Pratie or Seleting Proportions or Normal, heavyweight and Mass Conrete, Part 1, ACI Manual o Conrete praties.. Akhtaruzzaman, A. A and Hasnat, A. (1983), Properties o Conrete Using Crushed Brik as Aggregate, Conrete International, Vol. 5, No. 2, pp BS 8110 (1985), Strutural Use o Conrete: Code o Pratie or design and Constrution, Part 1. Khaloo, A. R. (1994), Properties o Conrete Using Crushed Clinker Brik as Coarse Aggregate, ACI Materials Journal, Vol. 91, No. 2, pp

10 52 M.A. Rashid et al. / Journal o Civil Engineering (IEB), 37(1) (2009) Mansur, M. A., Wee, T. H. and Cheran, L. S. (1999), Crushed Briks as Coarse Aggregate or Conrete, ACI Materials Journal, Vol. 96, No. 4, pp Neville, A. M. and Brooks, J. J. (2002), Conrete Tehnology, Pearson Eduation. Nilson, A. H. and Darwin, D. (1997), Design o Conrete Strutures Twelth Edition, MGraw- Hill Companies, In. Notations The ollowing symbols have been used in this study - = onrete ylinder ompressive strength, psi, tgt = targeted ylinder ompressive strength, psi u = onrete ube ompressive strength, psi r = modulus o rupture o onrete, psi E = seant modulus o elastiity o onrete, psi w = dry unit weight o onrete, p