ABRASION RESISTANCE OF CONCRETE AS INFLUENCED BY INCLUSION OF FLY ASH. Tarun R. Naik*, Shiw S. Singh**, and Mohammad M. Hossain***

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1 ABRASION RESISTANCE OF CONCRETE AS INFLUENCED BY INCLUSION OF FLY ASH Tarun R. Naik*, Shiw S. Singh**, and Mohammad M. Hossain*** *Director, **PostDoctoral Fellow, and ***Research Associate, Center for ByProducts Utilization, College of Engineering and Applied Science, Department of Civil Engineering and Mechanics, University of WisconsinMilwaukee, Milwaukee, WI, ABSTRACT This research was conducted to evaluate abrasion resistance of highvolume fly ash concrete. A reference plain portland cement concrete was proportioned to obtain 28 day strength of 41 MPa. Concrete mixtures were also proportioned to have two levels of cement replacements (50 and 70%) with an ASTM Class C fly ash. Abrasion tests were carried out using the rotating cutter method as per ASTM C944. In this work all the concrete specimens made either with or without fly ash passed the abrasion resistance requirements per ASTM C779, Procedure B. An accelerated test method was also developed to evaluate abrasion resistance of concrete. This method used the rotary cutter device having dressing wheels equipped with smaller size washers. A measured amount of standard Ottawa sand was added to the surface being abraded at one minute intervals. The accelerated test results exhibited lower abrasion resistance for highvolume fly ash concrete systems relative to nofly ash concrete. Introduction In general, inclusion of fly ash to concrete causes reduction in early age strength, but longterm strength and durability of fly ash concrete are generally higher than that of the plain portland cement concrete containing no fly ash.

2 Abrasion of concrete occurs due to rubbing, scraping, skidding or sliding of objects on its surface. The primary factors affecting the abrasion resistance of concrete are: compressive strength, aggregate properties, finishing method, use of toppings, and curing. Only a very limited amount of work has been done on abrasion resistance of concrete containing high volumes of Class C fly ash. This research work was undertaken to investigate the effects of inclusion of large amounts of fly ash on concrete resistance to abrasion. Previous Studies A number of studies have been conducted to develop fly ash concrete for structural application (1 9). Naik and Ramme (2,3) performed studies to develop mixture proportions for structural grade concrete using high proportions of an ASTM Class C fly ash. They concluded that fly ash can be used for structural grade concrete in quantities of up to at least 40 percent replacement of cement. Several studies have substantiated that highvolume fly ash concrete can be manufactured for structural applications (9). Tikalsky and Carrasquillo (4) reported that concrete containing Class C fly ash possessed superior abrasion resistance compared to either plain portland cement concrete or concrete containing Class F fly ash. Ukita et al. (5) showed that at a 30% cement replacement with a Class F fly ash, the abrasion resistance of fly ash concrete was lower relative to plain portland cement concrete. Barrow et al. (6) measured abrasion resistance of concrete made with fly ash having cement replacement between 0 and 35% by volume. They concluded that the concrete incorporating either Class C or Class F fly ash attained abrasion resistance equivalent to that of nofly ash concrete. Langan et al. (7) studied the influence of compressive strength on durability of concrete containing fly ash at a 50% cement replacement by weight. The authors concluded that the compressive strength does not seem to have a significant effect on abrasion resistance of concrete. Recently Bilodeau and Malhotra (8) determined abrasion resistance of highvolume Class F fly ash concretes. Their test result shows higher resistance to abrasion for nofly ash concrete as compared with highvolume fly ash concretes. Materials Experimental Program An ASTM C150 Type I cement, obtained from one source was used in this work. A Class C fly ash obtained from Pleasant Prairie Power Plant of Wisconsin Electric Power Company was used in this investigation. Chemical and physical properties of the fly ash were determined according to ASTM C618 (Tables 1 and 2). The fine aggregate was a natural sand with a 6.35 mm maximum

3 size, which was obtained from a local precast concrete producer. The coarse aggregate used in this study was 25 mm nominal maximum size containing a mixture of rounded and crushed limestone, which was also obtained from the same precast concrete producer. A commercially available superplasticizer (Daracem TM 100) was used to vary workability of concrete for a given watertocementitious material ratio. An airentraining agent (Catexol A.E. 260) was utilized to maintain air content at about 6±1%.

4 TABLE 1 Chemical Composition of Fly Ash Chemical Tests Fly Ash (%) ASTM C618 Specifications (%) Silicon Oxide, SiO 2 Aluminum Oxide, Al 2 O 3 Iron Oxide, Fe 2 O 3 Total, SiO 2 +Al 2 O 3 +Fe 2 O 3 Sulfur Trioxide, SO 3 Calcium Oxide, CaO Magnesium Oxide, MgO Titanium Oxide, TiO 2 Potassium Oxide, Ka 2 O Sodium Oxide, Na 2 O Moisture Content Loss on Ignition minimum 5.0 maximum 5.0 maximum 1.5 maximum 3.0 maximum 6.0 maximum TABLE 2 Physical Properties of Fly Ash Physical Tests Fly Ash ASTM C618 Specifications Fineness retained on No. 325 Sieve (%) Pozzolanic Activity Index with Cement (% of control) Water Requirement (% of control) max min max Autoclave Expansion (%) max Specific Gravity 2.78

5 Preparation of Test Specimens Concrete mixture proportions developed in this work are presented in Table 3. The ratio of fly ash addition to cement replaced was kept at The watertocementitious material ratio varied between 0.33 to 0.36, and desired workability was achieved through the aid of the superplasticizer. Specimens (150 x 300 mm) were cast for compressive strength measurement. Slab specimens of 300 x 300 x 100 mm were prepared for abrasion resistance measurement. These specimens were prepared in accordance with the applicable ASTM procedure. TABLE 3 Mixture Proportions Using ASTM Class C Fly Ash Mixture Number C3 P47 P48 Specified Design Strength (MPa) Cement (kg/m 3 ) Fly Ash (kg/m 3 ) Water (kg/m 3 ) WatertoCementitious Material Ratio Sand, SSD (kg/m 3 ) 25mm Aggregates, SSD (kg/m 3 ) Slump (mm) Air Content (%) Superplasticizer (L/m 3 ) Air Entraining Admixture (ml/m 3 ) Air Temperature ( C) Concrete Temperature ( C) Fresh Concrete Density (kg/m 3 ) Hardened Concrete Density (kg/m 3 ) Testing of Specimens Compressive strength of concrete was determined in accordance with ASTM C39. Abrasion tests were carried out using the rotary cutter method conforming to ASTM C944 requirements. The depth of wear was evaluated in accordance with ASTM C779, Procedure B. The rotary cutter method having a washer diameter equal to that of the dressing wheel produced a depth of abrasion of about 1 mm at 60 minutes of abrasion. In order to obtain relative abrasion resistance of concretes, especially highstrength, another method is needed which can apply higher abrasive forces than that exerted by the ASTM technique. Therefore, it was decided to develop a technique to amplify the depth of wear so that concretes having high resistance to abrasion can be evaluated in

6 a short period of time. An accelerated test method was developed to measure abrasion resistance of concrete. In this method, the rotary cutter apparatus was equipped with washers having a smaller diameter relative to the dressing wheels and equal amounts of sand (about a teaspoon) were added to the concrete surface during exposure to abrasion at one minute intervals. Depth of wear was measured according to ASTM C779, Procedure B. Strength Properties Test Results and Discussions Compressive strength data are presented in Figure 1. As anticipated, early age strengths of highvolume fly ash concrete mixtures were low, especially at 70% cement replacement with the fly ash. At 28day age, the 50% fly ash mixture attained strength required for structural applications, whereas the performance of the 70% fly ash mixture was unsatisfactory with respect to compressive strength at this age. However, the 70% fly ash mixture did develop strength in excess of 31 MPa at 91 days (Figure 1). Abrasion Resistance Initially all the concrete mixtures (C3, P47 and P48) that were tested according to ASTM C944 test method showed relatively small amounts of surface wear, about 1 mm of depth of wear and therefore, passed the abrasion resistance requirement per ASTM C779, Procedure B (10). The accelerated test method used in this work produced higher amounts of abrasion relative to the ASTM C944 test method. As expected, depth of wear increased with time of abrasion. Up to 55 minutes of abrasion time during the accelerated testing, the mixtures C3 (the reference mixture containing no fly ash) and P47 (50% cement replacement) exhibited abrasion depth less than 3 mm, and therefore did not fail per ASTM C779, Procedure B (Figures 2 through 4). Therefore, these mixtures have excellent abrasion resistance against high abrasive forces. However, when time of abrasion increased to 60 minutes, the fly ash concrete mixtures with 50% and 70% cement replacement showed depth of wear greater than 3 mm. In this work, abrasion resistance of the concrete was compared at a constant watertocementitious materials ratio, not at a constant compressive strength. This was done to determine the extent of abrasion damage when large volumes of cement is replaced with fly ash. For a given range of compressive strengths, it can be assumed that depth of wear (d w ) of concrete is inversely proportional to its compressive strength (f). The depth of wear, therefore, can be expressed by the following relation: or d w 1 f (1)

7 d w f = C (2) where C is a constant. For the accelerated testing work conducted in this work, below 30 MPa, the value of C was found to be 71 mmmpa. The values of C were 90 mmmpa for 30 to 50 MPa concretes and 114 mmmpa for 50 to 70 MPa concretes. For other methods of depth of abrasion resistance measurements, the value of the constant C should be determined using Equation 2 for each range strengths to achieve better results. The experimental values of depth of wear, and the calculated values from concrete strengths using Equation 2 for the 50% and 70% mixtures are presented in Figures 5 and 6. Additional experimental data obtained from the literature (11) is shown in Figure 7. The experimental values are nearly equal to the values derived from Eq. 2 (Figures 5 through 7). Therefore, if abrasion resistance is known at a particular strength level, then abrasion resistance at other levels can be estimated by Eq. 2 within a given compressive strength range. Conclusions The following main conclusions were drawn based on the results obtained in the present study. 1.Compressive strengths of highvolume fly ash concrete mixtures at 50 and 70 percent cement replacements were lower than the reference concrete containing no fly ash. However, the difference between strength gain of fly ash and nofly ash concrete diminished with age. Concrete mixture having 50% cement replacement with fly ash attained sufficient strength required for structural applications. 2.All the concrete mixtures used in this study, showed excellent abrasion resistance when tested in accordance with ASTM C The accelerated testing method developed in this work, produced higher depth of wear compared to the standard ASTM C944 test method. The rate of depth wear is suitable for accelerated testing of concretes having a wide range of abrasion resistance, especially structural and high strength concretes made with or without fly ash. 4.In general, the nofly ash concrete showed higher abrasion resistance during the accelerated testing relative to highvolume fly ash concrete mixtures. None of the concrete mixtures failed during the 30 minutes of abrasion in accordance with the ASTM C779, Procedure B criteria. However, when time of exposure to abrasion was increased to 60 minutes, the highvolume fly ash concrete mixtures showed depth of wear in excess of 3 mm at 28 days. But at 91 days all the concrete mixtures exhibited excellent abrasion resistance when tested in accordance with the accelerated testing method proposed. 5.Abrasion resistance of concrete was primarily influenced by its compressive strength. 6.For a given concrete compressive strength range, irrespective of the amount of fly ash, the products of depth of wear and compressive strength was found to be constant. Therefore,

8 for a known value of compressive strength in a particular strength range, depth of wear can be determined by Eq. 2, and Fig. 7.

9 FIG. 1 Compressive Strength Versus Percentage Fly Ash FIG. 2 Abrasion Resistance Data Obtained from the Accelerated Testing

10 of Concrete at 60 Minutes of Abrasion Time

11 FIG. 3 Abrasion Resistance Data Obtained from the Accelerated Testing of Concrete at 28Day Age FIG. 4 Abrasion Resistance Data Derived from the Accelerated

12 Testing of Concrete at 91Day Age

13 References 1.E.E. Berry and V.M Malhotra, "Fly Ash for Use in Concrete A Critical Review", ACI Journal, 77 (2), 5973 (1980). 2.T.R. Naik and B.W. Ramme, "Low Cement Content High Strength Structural Grade Concrete with Fly Ash", International Journal of Cement and Concrete Research, 17 (1), (1989). 3.T.R. Naik and B.W. Ramme, "High Strength Concrete Containing Large Quantities of Fly Ash", ACI Materials Journal, 86 (2), (1984). 4.P.J. Tikalsky and R.L. Carrasquillo, "Durability of Concrete Containing Fly Ash", Center for Transportation Research, Bureau of Engineering Research, University of Texas at Austin, Research Report: 3643, 141 (1986). 5.K. Ukita, S. Shigematsu, and M. Ishii, "Improvement in the Properties of Concrete Utilizing Classified Fly Ash", Proceedings of the Third International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Trondheim, Norway, V.M. Malhotra, Ed., 1 (ACI Special Publication SP114), (1989). 6.R.S. Barrow, K.M. Hadchiti, R.M. Carrasquillo and R.L. Carrasquillo, "Temperature Rise and Durability of Concrete Containing Fly Ash", Proceedings of the Third International Conference on the Use of Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Trondheim, Norway, V.M. Malhotra, Ed., 1 (ACI Special Publication SP114), (1989). 7.B.W. Langan, R.C. Joshi and M.A. Ward, "Strength and Durability of Concrete Containing 50% Portland Cement Replacement by Fly Ash and Other Materials", Canadian Journal of Civil Engineering, 17, 1927 (1990). 8.A. Bilodeau and V.M. Malhotra, "Concrete Incorporating High Volumes of ASTM Class F Fly Ashes Mechanical Properties and Resistance to Deicing Salt Scaling and to ChlorideIon Penetration", Proceedings of the Fourth International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Istanbul, Turkey, V.M. Malhotra, Ed., 1 (ACI Special Publication SP132), (1992). 9.T.R. Naik, S.S. Singh and W.Y. Hu, "HighVolume Fly Ash Concrete Technology", EPRI Report No. TR100473, (1992). 10.American Society for Testing and Materials, Annual Book of ASTM Standards, Sec. 4 Construction, 04.02, Concrete and Aggregates. 11.T.R. Naik, S.S. Singh and M.M. Hossain, "Abrasion Resistance of HighVolume Fly Ash Concrete System", CBU Report No. 176, Department of Civil Engineering and Mechanics, University of WisconsinMilwaukee, A Progress Report Submitted to EPRI, (1993). REP164A