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Journal of Scientific NATARAJA & Industrial Research & DAS: CEMENT BASED COMPOSITES WITH TILE WASTE AGGREGATES Vol. 70, May 2011, pp. 385-390
A simplified mix proportioning for cement based composites with crushed tile waste aggregate M C Nataraja* and Lelin Das Department of Civil Engineering, Sri Jayachamarajendra College of Engineering, Mysore 570 006, India Received 05 January 2011; revised 17 March 2011; accepted 21 March 2011 This study presents a procedure to proportion concrete mixes with tile waste as coarse aggregate. To arrive at water –cement ratio for matrix strength, generalized Abrams’ law is employed for proportioning and proper utilization of industrial wastes based on their engineering properties leading to the production of quality concrete through mix design. This also serves as a method for disposal of industrial tile waste through proper technology management. Keywords: Construction and demolition wastes, Tile waste, Abram’s law, Law of mixtures, Recycled aggregates
Introduction In India, large quantity of construction and demolition (C&D) waste, including substantial amount of used concrete paving blocks and tiles, is produced in metropolitan cities every year. C&D wastes are normally composed of concrete rubble, bricks, blocks and tiles, sand and dust, timber, plastics, cardboard and paper, and metals1. Crushed concrete paver blocks, tiles and bricks, after separation from other C&D waste and sieved, can be used as a substitute for natural coarse aggregates (CAs) in concrete or as a sub-base or a base layer in pavements or in the production of bricks and block1,2. Amount of CA in concrete also plays a role in controlling compressive strength (CS) of concrete3 . Recycled aggregates from coal combustion by products are being used in construction sectors4. Burks5 observed that many waste materials cannot be disposed off by incineration. A state-of - the- art review6 provides a brief description of marginal materials, their property characterization, and their potential applications. Gutt & Nixon7 discussed potential use of a wide spectrum of mining and quarry wastes in concrete. Crushed tile aggregate (CTA) is especially proposed for buildings constructed in hot climates. Elasticity modulus of concrete produced with CTA rubble was 70% of elasticity modulus of control concrete8. Both CS and tensile strength of CTA concrete *Author for correspondence E- mail:
[email protected]
were higher, but drying shrinkage was lower than control. Inclination of curve in ascending part of strain deformation diagrams was smaller and also deformation was higher compared to normal concrete due to CS9. Khaloo10 observed that CTA was 33% lighter in weight, and porosity and resistance to abrasion of CTA were smaller than control. The 28-day relative CS, tensile strength and flexural strength of CTA concrete were 0.93, 1.02 and 1.15 respectively10. This study presents a technique for using recycled aggregates obtained from broken clay tiles (Mangalore pattern) in non structural concrete. Experimental Section Tile waste is not as strong as conventional aggregate. As such, proportioning of trial mix was carried out as per comprehensive method11. According to generalized Abram’s Law12-15, relations for reproportioning mixes using different water-cement (w/c) ratio are given as S c for S0.5 ≥ 30MPa = − 0.2 + 0.6 for w S0.5
…(1)
S c = − 0.73 + 0.865 for S0.5 < 30MPa w S0.5
…(2)
where S0.5, CS at w/c ratio of 0.5; S, CS at any w/c ratio; and c/w, cement to water ratio.
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Table 1—Characteristics of materials used Materials Coarse aggregate
Type Waste broken tiles (20 4.75 mm)*
Properties Specific gravity Dry rodded density Water absorption Impact value Specific gravity Dry rodded density Water absorption Impact value Specific gravity Fineness modulus
Granite aggregate (20 - 4.75 mm)*
Fine aggregate
River sand
Test result 2.11 1130 kg/m3 7.02% 52.8% 2.60 1530 kg/m3 0.32 % 23.8 % 2.68 2.73
*Fraction 20 mm to 10 mm, 60%; and 10 mm to 4.75 mm, 40% Table 2—Trial mix details for broken tiles and granite aggregates as coarse aggregates by comprehensive method11 Parameters Concrete Water/cement (w/c) ratio Water content, kg/m3 Cement (C), kg/m3 Fine aggregate (FA), kg/m3 Coarse aggregate (CA), kg/m3 Aggregate/cement ratio Mortar mix W/C ratio FA/C ratio
W/C ratio used for trial mix was 0.5 and CA used was broken tile (BT). Another trial mix with conventional aggregate was proportioned and formed parallel series for comparison. CS of these mixes is intended to obtain response due to synergy between different ingredients of mixes. Since concrete is regarded as two component composite system, in addition to concrete strength at different ages, constituent mortar strength is also determined for the same w/c ratio with corresponding fine aggregate (FA)-cement ratio. Materials
BTs obtained from a local tile industry were crushed (size, < 20 mm) for use as CAs in concrete. Materials used include ordinary Portland cement of 43 grade conforming to IS: 8112-198916 with a 28-day CS of 52 N/mm2. Locally available river sand conforming to IS: 383-197017 was used as FA. CAs passing through 20 mm and retained on 4.75-mm sieve is the fraction used (Table 1). Potable water was used for mixing and curing. CONPLAST SP 430 super plasticizing admixture (sp gr, 1.22; and chloride content, nil) used is based on
Broken tile (BT)
Granite aggregate(GA)
0.5 190 380 879 720 4.2
0.5 190 380 788 975 4.63
0.5 2.31
0.5 2.07
sulphonated naphthalene polymers and is a brown liquid instantly dispersible in water. Casting, Curing and Testing
Casting and curing of specimens were done as per IS: 516-195918. For same w/c ratio and FA/c ratios as in trial mixes (Table 2), respective mortar cubes and concrete cubes were cast simultaneously. For all mixes considered in this study, 1% superplasticiser (by wt of cementitious material) was used while mixing and same was considered in calculation. CS development at w/c ratio of 0.5 was determined (Table 3) based on average of 5 samples tested at the age of 7 and 28 days, respectively: concrete (based on BT), 16, 27; concrete [based on granite aggregate (GA)], 20, 32; and mortar, 20, 35 MPa. Concrete cubes with BT as CA failed in aggregate crushing. CS of concrete was 14 MPa for mortar strength of 20 MPa at 7 days. At 28 days of curing, CS of concrete was 27 MPa against constituent mortar strength of 35 MPa at the same age. Normal failure mode of bond separation was observed in the case of crushed GA. It was observed that strength of
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Fig. 1—Bond failure and aggregate fracture during testing of: a) granite aggregate-GA; and b) tile aggregate-TA
Table 3—Trial mix details for broken tiles (25 & 30 MPa) as coarse aggregates Parameters
Broken tiles (25 MPa )
Broken tiles (30 MPa)
Concrete W/C ratio Water content, kg/m3 Cement, kg/m3 Fine aggregate (FA), kg/m3 Coarse aggregate (CA), kg/m3 Aggegate/cement ratio Mortar mix W/C ratio FA/C ratio Compressive strength, N/mm2 W/C ratio 7 Days 28 Days
0.54 204 377 842 720 4.14
0.45 204 453 782 720 3.32
0.54 2.23
0.45 1.72
0.54 Concrete 18.00 25.10
concrete and that of mortar strength was close both for 7 and 28 days of curing in the case of crushed GA. Fracture and Failure of Mortars and Concrete
Concrete, being a heterogeneous material, properties depend on properties and compatibility of individual components (CAs and mortar). Glaccio et al19 reported that all CA characteristic effects on concrete intensify only for aggregate (size > 5 mm). Concrete can attain strength of mortar matrix, only if strength of CA is higher than that of matrix. And hence crack propagation will be
0.45 Mortar 23.30 32.43
Concrete 22.24 29.14
Mortar 29.67 38.15
across periphery of CA. If strength of cement mortar is higher than CA fracture strength, due to lower modulus of deformation of CA than that of matrix, CAs can no longer transmit applied stress at the same deformation as that of mortar. Since stress in CA is greater than its strength, failure is through CA. A weak aggregate requires higher mortar strength for identical strength when compared with concrete experiencing bond failure. Failure around periphery of CAs and across CAs can be seen from broken cubes for GA (Fig. 1a) and tile aggregates (TA) (Fig. 1b).
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J SCI IND RES VOL 70 MAY 2011
Concrete as Composite Material
Once a unit cell model composed of mortar and CA is assumed, an effort can be directed to find mathematical relations such that appropriate properties of constituents can be computed. For limiting case of no bond, assumption of identical stresses in matrix and CAs is reasonable, if particles are more rigid than matrix. If particles are less rigid than matrix, as in the case of weak aggregate and high mortar matrix strength, bond is of less significance to composite behavior. CA experiences deformation of matrix up to its limit CS. For assumption of a perfect bonding between CA and matrix without any slippage at interface, strains experienced between CA, matrix, and concrete are the same. For a unit cell model, relation involving stress acting on each of the two phases (matrix, σm and CA, σa) loading and their volume fractions (matrix, vm and that of CA, va) is σc = σmvm+ σava …(3) for εc= εa=εm; vm + va =1 where σc, σm and σa are CS of concrete, matrix and CA respectively; vm & va are volume fraction of matrix and CA respectively; εc, εa, and εm are strains in concrete, aggregate and matrix respectively. To advance a generalized approach to proportion concrete mixes taking into account the characteristic strength of CA, possibility of using Eq. (3) for following assessments merits examination: i) From strength data of concrete, where aggregate fracture has been observed along with CS of constituent mortar matrix of that concrete for calculation of characteristic strength of CA; and ii) Using same law of mixtures with characteristic strength of CA known, calculation of required CS of mortar matrix for specific CS of concrete. For examination of above possibility, experimental data forms basis in this study. Results and Discussion Determination of Aggregate Characteristic Strength
In the case of specimens with BTs as aggregate since failure has been through crushing of aggregates, its contribution to strength development need be evaluated. To determine characteristic strength of aggregate, law of mixtures, as expressed in Eq. (3), is used. Thus, va = weight / specific gravity = 720/(2.11 x 1000) = 0.34 and vm = 1- 0.34 = 0.66.
CAs are crushed for 0.5 w/c ratio. Therefore, characteristic strength of aggregate of σa is to be found for the values of σc(0.5) and σm(0.5) as σ a = [σ c σmvm]/va = (26.96 - 35×0.66)/ 0.34 = 11.35 Mpa; therefore, σa = 11.35 MPa. With this characteristic strength, prediction of 7 day concrete strength is computed using Eq. (3) as σc =11.35×0.34 + 20×0.66 = 3.9 + 13.2 = 17.10 MPa as against 16 MPa experimentally obtained. Here matrix strength is greater than aggregate strength and hence iso-strain condition prevails. Concrete strength is lesser than constituent mortar strength observed by testing of trial mixes. Under such situation, following two possibilities merit examination: i) Technical feasibility to proportioning concrete mixes for concrete strength higher than characteristic strength of CA; and ii) Due to low characteristic strength of CA to optimize use of cement by limiting strength of concrete close to characteristic strength. Use of such concretes could be for nonstructural purposes. In this study, strengths of structural concretes examined are 25 MPa and 30 MPa. Low strength concretes are limited to 10 MPa and 15 MPa being close to characteristic strength of BT as CA. Reproportioned Mixes for 25 and 30 MPa
In order to compute combination of ingredients for 25 MPa and 30 MPa concretes with BT as CA, it is necessary to determine cement mortar matrix strength. For this, Eq. (3) is used as σm = [σc - σa va ]/ vm=[2511.35 x 0.34]/0.66 = 32 Mpa. W/C ratio for this 32MPa mortar strength is computed using Eq. (1) with reference to mortar strength of 35MPa at w/c ratio of 0.5 as
32 c = − 0.2 + 0.6 thus, w/c=0.54. 35 w Similarly for 30 MPa concrete, mortar strength is 39.5 MPa and corresponding w/c ratio would be 0.45 (Table 3). It has been observed that failure in both cases is by aggregate crushing. Mortar strengths have been far higher than characteristic strength of CA to realize strength contemplated. In order to obtain requisite mortar strength at calculated w/c ratios, cement contents are higher. This would lead to uneconomical situation in an effort to obtain structural strength of concrete. Hence only technical feasibility of compensating low characteristic strength of BT as CA is by commensurating mortar strength. Hence feasibility of obtaining low strength materials by limiting mortar strength and
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Table 4—Trial mix details for broken tiles (10 & 15 MPa) as coarse aggregates parameters Concrete W/C ratio Water content, kg/m3 Cement, kg/m3 Fine aggregate (FA), kg/m3 Coarse aggregate (CA), kg/m3 Aggregate/Cement ratio Mortar mix W/C ratio FA/C ratio Compressive strength, N/mm2 W/C ratio 7 Days 28 Days
Broken Tiles (10 MPa)
Broken Tiles (15 MPa)
0.78 204 262 943 720 6.34
0.67 204 304 906 720 5.35
0.78 3.6
0.67 2.98
0.78 Concrete 6.69 11.14
consequently controlling cement content is examined for concrete strengths of 10 and 15MPa. Reproportioned Mixes for 10 and 15 MPa
In proportions determined for 28 days strength of concrete with BT for 10 MPa and 15 MPa (Table 4), since concrete strength is close to characteristic strength of BT aggregate, distinct failure of concrete by crushing of aggregate is unlikely to take place. Hence w/c ratios are directly calculated by Eq. (2). Reference value of strength at 0.5 w/c ratio corresponds to concrete strength with BT is 27 MPa. W/C ratio for 10 MPa concrete, computed by Eq. (2) taking S0.5 strength as 27 MPa, is found to be 0.78. Similarly for 15 MPa concrete, w/c ratio would be 0.67. Quantities of ingredients (Table 3) of above two mixes arrive by following comprehensive approach11. For w/c ratio of 0.78, failures did not occur with aggregate crushing, and for w/c ratio of 0.67, failure was by partial crushing of aggregates. This is in order since mortar strength for w/c ratio of 0.78 was not very different from that of characteristic strength of tiles, whereas in the case of w/c ratio of 0.67, mortar strength was considerably higher than characteristic strength of tiles (11.35 MPa). Stepwise Procedure to Handle Low Strength Coarse Aggregate
Procedure to handle low strength CA is as follows: i) Fix water cement ratio of 0.5 for trial mix and water content of mix; ii) For maximum size and gradation of unconventional CA, obtain specific gravity and bulk density in saturated surface dry condition (SSD) and determine fineness modulus of FA; iii) Arrive at proportions of different constituents by absolute volume
0.67 Mortar 7.80 13.08
Concrete 9.76 16.30
Mortar 13.10 20.23
method of ACI20; iv) Arrive at proportions of constituent mortar with same water cement ratio and FA/C ratio; v) Calculate volume fractions of mortar and that of CA, cast and cure concrete and mortar specimens for different periods and determine their average CS; vi) Observe and categorize mode of failure such as predominantly bond failure or by crushing of aggregate, compare strength of concrete with that of constituent mortar at the same age and if failure is by crushing of CA and strength of mortar is greater than that of concrete strength then it can be inferred that characteristic strength of CA is lesser than that of mortar strength; vii) Calculate σa by use of law of mixtures with known values of vm and va, and σc and σm from σc = σava + σmvm; viii) To reproportion concrete mix for strength greater than characteristic strength of CA, mortar strength has to be higher than that of concrete strength, hence determine σm, required to obtain σc, from Eq. (3); ix) To reproportion concrete with BT for strength closer to characteristic strength of BT, mortar strengths need not be calculated from linear law of mixtures, and W/C ratios required are directly calculated from appropriate equations of generalized Abrams’ Law14,15; x) To obtain mortar strength, w/c ratio is calculated from any of Eqs (1) and (2) depending upon mortar strength greater or lesser than 30 MPa; xi) Keeping CA content same and for w/c ratio, calculate reproportion constituents of mix using absolute volume method20, and for the same w/c ratio and FA cement ratio calculate constituent mortar specimens are also cast; xii) Determine CS of concrete and compare value obtained with that specified; and xiii) Obtaining calculated mortar strength reinforces the approach resorted to obtain specified concrete strength.
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Conclusions This investigation determines constituent mortar strength along with that of constituent concrete strength when unconventional CAs are used. Trial concrete and mortar mixes are proportioned at w/c ratio of 0.5 to obtain synergy of all concrete ingredients due to interfacial bond and/or characteristic strength of CAs. When strength of mortar is greater than that of concrete strength, it is likely that failure would be predominantly by aggregate crushing. For specified strength of concrete, which is higher than that of characteristic strength of aggregate, compatible mortar strength is calculated by linear law of mixtures. To obtain that mortar strength, w/c ratio is calculated by generalized Abrams’ Law. BT taken as CAs can be used in place of conventional aggregates, provided, BT are proportioned in systematic way, though not for structural concrete economically. By limiting strength of concrete close to characteristic strength of BT, it would be possible to restrict mortar strength to minimize use of cement.
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