Center for By-Products Utilization

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1 Center for By-Products Utilization SHRINKAGE OF CONCRETE WITH AND WITHOUT FLY ASH By Tarun R. Naik, Yoon-moon Chun, and Rudolph N. Kraus Report No. CBU REP-596 January 27 For Presentation and Publication at the Ninth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Poland, May - June 27. Department of Civil Engineering and Mechanics College of Engineering and Applied Science THE UNIVERSITY OF WISCONSIN-MILWAUKEE

2 by Tarun R. Naik, Yoon-moon Chun, and Rudolph N. Kraus Synopsis: Cracking of concrete decks and pavements due to autogenous shrinkage and drying shrinkage leads to higher maintenance costs and shorter service life of the concrete. Use of shrinkage-reducing admixtures (SRAs) can reduce the shrinkage of concrete. This research was conducted to study the shrinkage of no-ash concrete and fly ash concrete as influenced by SRA use. A polyoxyalkylene alkyl ether based SRA was used at %, 1.8%, and 2.5% by mass (, 1.8, and 2.5 L/1 kg) of cementitious materials in concrete mixtures. The fly ash concrete was made by replacing 3% (by mass) of cement with Class C fly ash. In most cases, the SRA had an effect similar to water-reducing admixtures and often improved the strength of concrete. The SRA eliminated much of the initial drying shrinkage of concrete. The 4-day drying shrinkage was reduced by up to 8 to 85%, and the 28-day drying shrinkage reduced by up to 48 to 63%. When compared with the no-ash concrete, use of 3% Class C fly ash had the following effects: (a) autogenous shrinkage of concrete was lower at early ages and higher at later ages; (b) drying shrinkage of concrete (subsequent to 28 days of moist curing) was somewhat higher; and (c) a higher dosage of SRA was required to achieve comparable drying shrinkage. Keywords: air content; autogenous shrinkage; concrete; drying shrinkage; initial setting time; shrinkage-reducing admixtures; compressive strength. 1 MS# MF#12. FINAL. January 27.

3 Tarun R. Naik, CI, is a Professor of Structural Engineering and Academic Program Director of the UWM Center for By-Products Utilization (UWM-CBU) at the University of Wisconsin - Milwaukee. He is a member of ACI Committees 123, Research; 229, Controlled Low-Strength Materials (CLSM); 232, Fly Ash and Natural Pozzolans in Concrete; and 555, Concrete with Recycled Materials. He is also a member of ACI Board Advisory Committee on Sustainable Development. He was also Chairman of the ASCE Technical Committee on Emerging Materials (1995-2). Yoon-moon Chun is a postdoctoral fellow at the UWM-CBU. His research interests include the use of coal fly ash, coal bottom ash, and used foundry sand in concrete and masonry units, the use of fibrous residuals from pulp and paper mills in concrete; autogenous shrinkage of concrete; and self-consolidating concrete. ACI member Rudolph N. Kraus is Assistant Director of the UWM-CBU. He has directed numerous projects on the use of fly ash, bottom ash, used foundry sand, and wood ash in concrete, CLSM, and masonry units. Mr. Kraus has also directed research on selfconsolidating concrete and the use of fibrous residuals from the pulp and paper industry in concrete. INTRODUCTION Concrete is one of the most durable construction materials. However, cracking adversely affects its durability, functionality, and appearance. A major cause of cracking is related to shrinkage-induced strains, creating stresses when concrete is restrained. The shrinkage of concrete is often attributed to drying of the concrete over a long period of time, and recent observations have also focused on early age autogenous shrinkage problems. Cracked concrete typically needs to be repaired to prevent further deterioration due to freezing and thawing, and corrosion of steel reinforcement resulting from infiltration of water with or without chloride ions from de-icing salts. The cracking leads to additional costs for repair to prevent premature deterioration of the concrete and the corrosion of reinforcement steel. Cracking can significantly reduce the service life of concrete bridge decks, pavements, and other concrete structures. Use of shrinkage-reducing admixtures (SRAs) is advocated as one of the most effective ways of reducing shrinkage cracking. References on SRAs in technical literature trace their origin to Japan during the 198s. SRA composition varies depending on the manufacturer, but it generally consists of a surface-active organic polymer solution. SRAs are designed with the specific aim of reducing the surface tension of the pore solution. The reduction in capillary tension within the pore structure decreases the concrete volume changes due to internal self-desiccation or air drying of concrete [1, 2]. Ribeiro and associates [1] have reported effectiveness of SRAs on different concrete mixtures using two SRA products at different dosage rates. All the mixtures were 2 MS# MF#12. FINAL. January 27.

4 prepared by replacing 25% of cement with fly ash. Their study showed a maximum reduction in drying shrinkage of about 3% with the use of the maximum dosage of SRA. Roncero and associates [2] evaluated the influence of SRA on the microstructure and long-term behavior of concrete. In their study, concrete mixtures were prepared at.4 W/C and with % (reference), 1%, and 2% of SRA by mass of cement. After two years of drying at 5% relative humidity, the drying shrinkage strain reduced by about 26% and 51% for the concrete mixtures made with 1% and 2% of SRA, respectively, compared to the reference mixture (% SRA). On the other hand, in sealed condition, a slight expansion was observed for both the 1% and 2% SRA concrete mixtures. The reference concrete mixture showed autogenous shrinkage, especially during the first three weeks. A reduction in compressive strength was observed with incorporation of SRA. Bentz and associates [3] reported that the use of SRAs could increase the setting time and reduce the compressive strength of concrete, and adversely affect the air-void system in concrete. Berke and associates [4] have studied the performance of concrete containing a glycol-ether based SRA. The aim of their study was to produce concrete with good quality air-void systems needed for freezing and thawing resistance, while reducing shrinkage with the SRA. Their results showed that good air-void systems were obtainable with judicious use of the SRA. The major objective of this research was to evaluate the effectiveness of three different SRAs for reducing the autogenous shrinkage and drying shrinkage of concrete mixtures made with and without fly ash. The effects of SRAs on the slump, air content, initial setting time, compressive strength, and other properties of concrete were also evaluated. This paper reports part of the results on one of the three SRAs evaluated. A comprehensive report for the research is available elsewhere [5]. MATERIALS In this research, ASTM Type I portland cement. The Blaine specific surface of cement was 364 m 2 /kg. The strength of cement mortar (ASTM C 19) was 14.3, 24.8, 3.3, and 38.8 MPa at 1, 3, 7, and 28 days, respectively. The chemical composition of the cement was 2.2% SiO 2, 4.5% Al 2 O 3, 2.6% Fe 2 O 3, 64.2% CaO, 2.5% MgO, 2.4% SO 3,.53% total alkalies as Na 2 O, 1.4% loss on ignition,.4% insoluble residue, and 1.5% free lime. ASTM Class C fly ash was used for this research. The fly ash had the following properties: strength activity index (ASTM C 311) of 98% and 99% of Control mortar at 7 and 28 days, respectively; water requirement of 91% of Control; and density of 2.53 g/cm 3. The oxides composition of fly ash was 36.2% SiO 2, 19.% Al 2 O 3, 5.6% Fe 2 O 3, (6.8% SiO 2 + Al 2 O 3 + Fe 2 O 3,) 23.4% CaO, 3.7% MgO, 2.1% SO 3, 1.% Na 2 O, and 1.% K 2 O. 3 MS# MF#12. FINAL. January 27.

5 Natural sand (1.4% absorption, 2.66 specific gravity, 179 kg/m 3 bulk density) was used. The coarse aggregate used was crushed quartzite stone having a nominal maximum size of 19 mm. The coarse aggregate met the grading requirements for the WisDOT Size No. 1 (equivalent to AASHTO No. 67). The coarse aggregate had.4% absorption, 2.66 specific gravity, and 155 kg/m 3 bulk density. A polyoxyalkylene alkyl ether based SRA was used for the concrete mixtures reported in this paper. TEST METHODS Concrete was tested for the following fresh properties: slump (ASTM C 143), density (ASTM C 138), air content (ASTM C 231), and temperature (ASTM C 164). In addition, each concrete mixture was tested for time of initial setting (ASTM C 43 using two specimens), autogenous shrinkage (using three mm beams), compressive strength (ASTM C 39 using three 1 2 mm cylinders per age), and drying shrinkage (ASTM C 157 using three mm beams). The autogenous shrinkage was determined in accordance with a test method adapted from a procedure originally drafted by the Japan Concrete Institute [6]. In total three autogenous length-change comparators were built. Each comparator was built using two dial indicators and an invar rectangular bar connecting the two ends. In addition, a separate invar reference bar was prepared, and its length-change was measured using each comparator, periodically. The length-change of the reference bar was very small (± 1 microstrain) meaning that the comparator readings were reliable. To prepare concrete beam specimens for autogenous length-change, gage plugs (pins) and sealed plastic film molds (liners) were placed in steel beam molds. Then fresh concrete was placed and consolidated in the plastic molds, and covered with film covers and sealed with tape. The measurements for the autogenous length-change and temperature of concrete started at the time of initial setting of concrete. Additional measurements were taken once between 15 to 18 hours (approximately.7 days), and again at 24 hours. During the first 24 hours, the test setup was not disturbed; the dial indicators of each length-change comparator remained in contact with the gage plugs of each beam. Then hardened concrete beams were removed from molds and sealed with aluminum adhesive tape to prevent evaporation. After this, additional measurements were taken at the ages of 3, 7, 14, 28, and 56 days. Fig. 1 shows the testing of a hardened, sealed concrete beam for autogenous length-change. More details are available elsewhere [5] on the test setup and methods used in this research for determining autogenous length-change of concrete. RESULTS AND DISCUSSIONS Mixture proportions and time of initial setting Concrete mixtures were made using mid-range water-reducing admixture (MRWRA- 3), air-entraining admixture (AEA-3), and shrinkage-reducing admixture (SRA-3). Three dosage rates of SRA were used: (1) zero (reference); (2) the average dosage rate of 1.8 L/1 kg of cementitious materials (average of the minimum rate [1. L/1 kg of Cm] and the maximum rate recommended by the SRA manufacturer); and (3) the maximum 4 MS# MF#12. FINAL. January 27.

6 recommended dosage rate of 2.5 L/1 kg of cementitious materials. The reference (base) concrete mixtures were: (1) Wisconsin Department of Transportation (WisDOT) Grade A (no fly ash) and (2) WisDOT Grade A- (fly ash replacing 3% of cement). Table 1 shows the mixture proportions and fresh properties of concrete mixtures. Test specimens of concrete were made and cured according to the ASTM Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory (C 192). The design W/Cm (water-cementitious materials ratio) of concrete was.4. Use of SRA-3 reduced either the MRWRA-3 demand (Mixtures 1.8 and 2.5 Vs..), or both the MRWRA-3 demand and W/Cm (Mixtures 1.8- and 2.5- Vs..-) in concrete mixtures, meaning that SRA-3 had a water-reducing effect. Overall, use of fly ash reduced the MRWRA-3 demand (Mixtures.- Vs..; and Mixtures 2.5- Vs. 2.5). The target air content was 6 ± 1.5%. When SRA-3 was used at its average dosage rate, the AEA-3 demand was slightly higher than that of the reference (no SRA) concrete mixtures. When SRA-3 was used at its maximum dosage rate, the AEA-3 demand increased significantly. The AEA-3 dosage itself was small (.39 L/m 3 of concrete, or.12 L/1 kg of Cm) regardless of the SRA-3 dosage. The time of initial setting of concrete was determined for starting the measurements for autogenous shrinkage. The time of initial setting of the reference (no SRA) Grade A- fly ash concrete was exceptionally long (15 hours) (Table 1); the reason for this is not known. The rest of the concrete mixtures made with chemical admixtures from Source 3 showed an initial setting time of 7 to 8.5 hours. Autogenous shrinkage Table 2, and Fig. 2 to Fig. 5 show the autogenous shrinkage of concrete containing chemical admixtures from Source 3. Use of SRA-3 was somewhat helpful in reducing the autogenous shrinkage of Grade A no-ash concrete mixtures up to the age of 28 days (Fig. 2). SRA-3 was effective in reducing the autogenous shrinkage of Grade A- fly ash concrete mixtures, especially at later ages of 28 and 56 days (Fig. 3). In comparison with Grade A no-ash concrete mixtures, Grade A- fly ash concrete mixtures generally showed a lower autogenous shrinkage at ages of up to 14 days, but showed either a similar or higher autogenous shrinkage at 28 and 56 days (Fig. 4, Fig. 5). Drying shrinkage The test results for drying shrinkage of concrete (subsequent to 28 days of moist curing) are shown in Table 3 and Table 4, and Fig. 6 to Fig MS# MF#12. FINAL. January 27.

7 Grade A no-ash concrete mixtures containing SRA-3 (Mixtures 1.8 and 2.5) showed a much lower drying shrinkage than their reference (no SRA) concrete mixture (Fig. 6), especially at early ages. Beyond a SRA-3 dosage rate of 1.8 L per 1 kg of cement, a further reduction in drying shrinkage was not achieved. Rather, the drying shrinkage increased slightly when the SRA-3 dosage rate increased from 1.8 to 2.5 L per 1 kg of cement. SRA-3 was also quite effective in reducing the drying shrinkage of Grade A- fly ash concrete mixtures (Fig. 7), especially at early ages. The reduction was almost proportional to the SRA-3 dosage rate of up to at least 2.5 L per 1 kg of cementitious materials. The data lines were nearly parallel between the air-storage periods of 4 days and 112 days. Overall, for a SRA-3 dosage rate of up to 1.8 L/1 kg of cementitious materials, Grade A- fly ash concrete mixtures showed either approximately the same or a somewhat higher drying shrinkage than their Grade A no-ash counterparts (Fig. 8, Fig. 9). But when the SRA-3 dosage rate increased to 2.5 L/1 kg of cementitious materials, the drying shrinkage of the fly ash concrete 2.5- was about the same as that of its noash counterpart, Mixture 2.5. Compressive strength The test results for compressive strength of concrete are shown in Table 5. SRA-3 did not affect the compressive strength of Grade A no-ash concrete mixtures. Due to their relatively low W/Cm, the Grade A- fly ash concrete mixtures containing SRA-3 showed somewhat higher compressive strength than their reference (no SRA) Grade A- fly ash concrete mixture. SRA-3 itself does not seem to have affected the compressive strength of concrete considerably. Compared with Grade A no-ash concrete mixtures, Grade A- fly ash concrete mixtures showed a lower compressive strength at ages of up to 14 days, and a similar compressive strength at 28 days and beyond. CONCLUSIONS Based on the test results obtained from this experimental program, the following conclusions are drawn: 1. As for the effect of fly ash on autogenous shrinkage, compared with Grade A no-ash concrete mixtures, Grade A- fly ash concrete mixtures (with and without SRA) usually exhibited a lower autogenous shrinkage at early ages and then a higher autogenous shrinkage starting from 14 to 56 days. 2. Drying shrinkage: 6 MS# MF#12. FINAL. January 27.

8 (a) The drying shrinkage reduced approximately in direct proportion to the amount of SRA used. When SRA is used in excess of certain dosage rates, drying shrinkage may not reduce any further. (b) SRA was most effective in reducing the drying shrinkage of concrete during early periods (up to about four days) of exposure to dry air when the rate of drying shrinkage is otherwise the highest. In effect, SRAs eliminated much of the initial high drying shrinkage of concrete. (c) By using SRAs in Grade A and A- concrete mixtures, the 4-day drying shrinkage was reduced by up to 8 to 85%, and the 28-day drying shrinkage reduced by up to 48 to 63%. (d) Compared with Grade A no-ash concrete, Grade A- fly ash concrete generally showed a slightly higher drying shrinkage when using the same SRA dosage and required more SRA to achieve similar drying shrinkage. 3. Many times, SRA-3 had an effect similar to water-reducing admixtures and significantly reduced the required amounts of mid-range water-reducing admixture (MRWRA-3). When SRA-3 was used at its maximum dosage, it increased the AEA- 3 demand. 4. SRA-3 did not affect the compressive strength of Grade A no-ash concrete mixtures. Due to their relatively low W/Cm, the Grade A- fly ash concrete mixtures containing SRA-3 showed somewhat higher compressive strength than their reference (no SRA) Grade A- fly ash concrete mixture. ACKNOWLEDGEMENTS The funding for this project was provided by the Wisconsin Department of Transportation (WisDOT) and the Federal Highway Administration (FHWA) thorough the Wisconsin Highway Research Program (WHRP). The authors express their deep gratitude for the support. The UWM Center for By-Products Utilization was established in 1988 with a generous grant from the Dairyland Power Cooperative, La Crosse, WI; Madison Gas and Electric Company, Madison, WI; National Minerals Corporation, St. Paul, MN; Northern States Power Company, Eau Claire, WI; We Energies, Milwaukee, WI; Wisconsin Power and Light Company, Madison, WI; and, Wisconsin Public Service Corporation, Green Bay, WI. Their financial support and additional grant and support from Manitowoc Public Utilities, Manitowoc, WI, are gratefully acknowledged. REFERENCES 1. Ribeiro, A. B., Carrajola, A., and Gonçalves, A., 23, Effectiveness of Shrinkage- Reducing Admixture on Different Concrete Mixtures, Supplementary Papers of the 7 MS# MF#12. FINAL. January 27.

9 Seventh CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, Berlin, Germany, pp Roncero, J., Gettu R., and Martin M. A., 23, Evaluation of the Influence of a Shrinkage Reducing Admixture on the Microstructure and Long-Term Behavior of Concrete, Supplementary Papers of the Seventh CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, Berlin, Germany, pp Bentz, D. P., Jensenm, O. M., and Geiker, M., 22, On the Mitigation of Early Age Cracking, Self-Desiccation and Its Importance in Concrete Technology, Lund, Sweden, < pp Berke, N. S., Li, L., Hicks, M. C., and Bae, J., 23, Improving Concrete Performance with Shrinkage-Reducing Admixtures, Proceedings of the Seventh CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, ACI SP-217, Berlin, Germany, pp Naik, T. R., Chun Y.-m., and Kraus, R. N., 26, Reducing Shrinkage Cracking of Structural Concrete Through the Use of Admixtures, Report No. CBU-25-2, Final Report Submitted to the Wisconsin Department of Transportation, March. 6. JCI (Japan Concrete Institute), 1998, Autogenous Shrinkage of Concrete, Proceedings of the International Workshop Organized by JCI, Hiroshima, Japan, E & FN Books, London and New York, 411 pp. 8 MS# MF#12. FINAL. January 27.

10 Table 1 Mixture Proportions, Fresh Properties, and Time of Initial Setting of Concrete Mixture designation* Cement (kg/m 3 ) Class C fly ash (kg/m 3 ) Water (kg/m 3 ) Fine aggregate, SSD (kg/m 3 ) Coarse aggregate, 19 mm, SSD (kg/m 3 ) Mid-range water-reducing admixture (L/m 3 ) Air-entraining admixture (L/m 3 ) Shrinkage-reducing admixture (L/m 3 ) W/Cm Slump (mm) Air content (%) Air temperature ( C) Concrete temperature ( C) Density (kg/m 3 ) Time of initial setting (hours) * The number following indicates the approximate dosage rate of SRA in L/1 kg of cementitious materials. The manufacturer s recommended dosage range of SRA-3 was % by mass of cementitious materials ( L/1 kg of Cm). means that fly ash was used to replace 3% of cement (WisDOT Grade A- concrete). Table 2 Autogenous Shrinkage of Concrete Age (days) Autogenous shrinkage* * at time of initial setting. -: Expansion. +: Shrinkage. 9 MS# MF#12. FINAL. January 27.

11 Table 3 Drying Shrinkage of Concrete Subsequent to 28 Days of Moist Curing Air-storage period Drying shrinkage subsequent to 28 days of moist curing (days) Average Table 4 Relative Reduction in Drying Shrinkage of Concrete Air-storage period Relative reduction in drying shrinkage (%) subsequent to 28 days of moist curing (days) Average Table 5 Compressive Strength of Concrete Age (days) Compressive strength (MPa) MS# MF#12. FINAL. January 27.

12 Fig. 1 Testing of a hardened, sealed beam for autogenous length-change 25 No Fly Ash Autogenous Shrinkage SRA-3 (L/1 kg of Cm) 56-day 28-day 14-day 7-day 3-day 1-day.7-day Fig. 2 Autogenous shrinkage of Grade A no-ash concrete vs. SRA dosage rate Autogenous Shrinkage Fly Ash SRA-3 (L/1 kg of Cm) 56-day 28-day 14-day 7-day 3-day 1-day.7-day Fig. 3 Autogenous shrinkage of Grade A- fly ash concrete vs. SRA dosage rate 11 MS# MF#12. FINAL. January 27.

13 Autogenous Shrinkage Age (days) Fig. 4 Autogenous shrinkage of Grade A no-ash concrete and Grade A- fly ash concrete vs. age 4 Autogenous Shrinkage Mixture Designation day 28-day 14-day 7-day 3-day 1-day.7-day Fig. 5 Autogenous shrinkage of no-sra concrete and SRA concrete vs. fly ash content Drying Shrinkage subsequent to 28 days of moist curing No Fly Ash SRA-3 (L/1 kg of Cm) Average 112-day 56-day 28-day 14-day 7-day 4-day Fig. 6 Drying shrinkage of Grade A no-ash concrete vs. SRA dosage rate 12 MS# MF#12. FINAL. January 27.

14 Drying Shrinkage subsequent to 28 days of moist curing Fly Ash SRA-3 (L/1 kg of Cm) Average 112-day 56-day 28-day 14-day 7-day 4-day Fig. 7 Drying shrinkage of Grade A- fly ash concrete vs. SRA dosage rate Drying Shrinkage subsequent to 28 days of moist curing Air-Storage Period (days) Fig. 8 Drying shrinkage of Grade A no-ash concrete and Grade A- fly ash concrete vs. air-storage period Drying Shrinkage subsequent to 28 days of moist curing day 56-day 28-day 14-day 7-day 4-day Mixture Designation Fig. 9 Drying shrinkage of no-sra concrete and SRA concrete vs. fly ash content 13 MS# MF#12. FINAL. January 27.