High Early Strength Fly Ash Concrete for Precast/Prestressed Products

Presents field applied research to report the advantages of using a high quality ASTM C-618 Class C fly ash on water de­ mand, workability and compressive strength of concrete. The research was performed at two precast/prestressed concrete plants to identify optimum mixture proportions for production of high early strength concrete with high fly ash contents. Tests were carried out on nominal 5000 psi (34 MPa) concrete utiliz­ ing fly ash produced at Wisconsin Electric Power Company's Pleasant Prairie Power Plant. Fly ash replacement improved workability, decreased water demand, and increased strength Tarun R. Naik while maintaining the high early strength requirements of pre­ Associate Professor of Civil Engineering cast/prestressed concrete operations. Director, Center for By-Products Utilization Department of Civil Engineering and Mechanics Milwaukee, Wisconsin he purpose of this project was to pavement construction and other proj­ develop mixture proportioning ects have successfully used structural Tinformation for the production of grade concrete with up to 70 percent ce­ high early strength concrete with high ment replacement. fly ash content for precast prestressed The objective of this paper is to re­ concrete products. The fly ash used in port that high early strength concrete this project was produced by Wisconsin can be produced with high replacement Electric Power Company (WE) at the of cement by fly ash for precast/pre­ Pleasant Prairie Power Plant located in stressed concrete operations. Effects of Kenosha County, Wisconsin. This fly fly ash content on water demand and ash meets the Class C requirements of workability are also reported. ASTM C-618. Tests were carried out on nominal Test data from mixture proportioning 5000 psi (34 MPa) 28-day compressive 1 5 reported in earlier publications · strength concrete, where fly ash was clearly established that this source of substituted for cement at levels up to 30 Bruce W. Ram me fly ash can be used for structural grade percent replacement on a 1.25 to 1.00 Senior Project Manager concrete in quantities.of up to 60 per­ fly ash replacement for cement basis. A Engineering and Construction Department cent replacement of cement. Demon­ literature search was also conducted to Wisconsin Electric Power Company stration projects are also reported in further study the water demand, work­ Milwaukee, Wisconsin these publications which show that ability and strength characteristics for

72 PCI JOURNAL fly ash concrete. Rather than compiling Table 1. Chemical and physical properties test data. an exhaustive annotated bibliography Pleasant Prairie Power Plant (Class C fly ash). of the available literature, some impor­ tant publications were reviewed and are Number Range Avg. ASTM 1 24 Chemical composition of samples (percent) (percent) C-618 listed in the references. - Silicon oxide (Si02) 9 32.90- 35.60 34.39 - PLEASANT PRAIRIE Aluminum oxide (AI20 3) 9 17.10-18.20 17.74 - CLASS C FLY ASH Iron oxide (Fe20 3) 9 15.10- 6.30 5.93 - Total (Si02+Al203) 9 55.70-59.30 58.07 50.0min. The Pleasant Prairie Power Plant Sulfur trioxide (S03) 9 2.68- 3.42 3.08 5.0max. Class C fly ash is a by-product of West­ Calcium oxide (CaO) 9 26.60- 28.60 27.52 - em United States sub-bituminous coal Moisture content 9 0.04- 0.44 0.12 3.0max. combustion. The fly ash is captured by Loss on ignition 9 0.20- 0.63 0.39 6.0max. electrostatic precipitators from flue gas Magnesium oxide (MgO) 7 4.10- 4.80 4.56 5.0max. prior to discharge through exhaust Available alkalies as Na20 7 0.87- !.'55 1.19 1.5 max. chimneys, and meets the requirements of ASTM C-618 for Class C fly ash Number ASTM (see Table 1). Until about 10 years ago, Physical Test of samples Range Avg. C-618 most of the fly ash available from coal Fineness, percent retained on burning power plants in the United #325 wet sieve 9 11.03- 13.34 18.83 34.0max. States was of the Class F (low calcium) Pozzolanic activity index: variety. However, the introduction of With cement, 28 days, percent 9 91- 133 Ill 75.0min. low sulphur sub-bituminous coal in the Pozzolanic activity index: 1970s made Class C (high calcium) fly With lime, 7 days, psi 9 810-1486 1029 800min. ash more readily available. Water requirement, percent of Class C fly ash has a higher lime con­ the control 9 88-92 89 105 max. tent than Class F fly ash and possesses Soundness: some cementitious properties of its Autoclave expansion (percent) 9 0.07-0.21 0.13 0.8 max. own. Therefore, this Class C fly ash can Specific gravity 9 2.55-2.71 2.66 - be used in higher proportions than the 15 to 20 percent range typically used for the Class F fly ash for structural SPECIMEN PREPARATION 2, were cured with the prestressed quality concrete. AND TESTS member where the test concrete was used for casting it. The remaining cyl­ Each batch of concrete produced was MIX PROPORTIONING inders were cured in a protected area tested for acceptability before concrete away from the prestressing bed and Mix proportions were developed for tests were undertaken. Fresh concrete traffic. Each cylinder was covered with producing concrete on a 1.25 to 1.00 fly tests including slump and air content a plastic bag which had a rubber band ash to cement weight substitution basis. were performed and mix proportions around it. A Type I cement was used and the re­ were recorded (see Tables 2 and 3). At­ Cylinders from both plants were placement quantities were 0, 10, 15, 20, tention was also paid to maintaining taken to the laboratory the next day. 25 and 30 percent. Twelve different constant workability, which is not en­ They were then stripped, marked and mixture proportions were developed tirely evident from the slump values be­ stored in a lime-saturated water bath based upon a nominal 5000 psi (34 cause of the use of a superplasticizer in until the time of their tests. Cylinders MPa) control mixture that contained no the concrete. From each concrete mix­ for the very early age strength test were fly ash. Mixture proportions and test ture, standard specimens were prepared tested after stripping them. data for the 12 mixes are given in Ta­ for compressive strength tests. bles 2 and 3. TEST RESULTS CONCRETE MIXING CURING AND DISCUSSION Concrete was produced at two differ­ Cylinders were cured following the Compressive Strength ent precast/prestressed concrete plants actual practice of the individual pre­ The compressive strength results are 3 in 2 cu yd (1.5 m ) test batches. Based cast/prestressing plant. For Plant No. 1, shown in Tables 4 and 5. Figs. I and 2 on the preliminary mixture proportions all cylinders were cured under a plastic show the compressive strength vs. age developed, the final mixture propor­ sheet after the tops of these cylinders comparison for the 5000 psi (34 MPa) tions were completed after consultation were sprayed with a liquid curing com­ concrete mixtures produced at the two with the concrete producers. Standard pound. They were cured in the open air different prestressing plants. The re­ hatching and mixing procedures for on top of a prestressing bed which was sults represent the testing of two cylin­ ready mixed concrete were followed, in not being used at the time. ders at each test age as opposed to the accordance with ASTM C-94. Early age test cylinders, at Plant No. more common testing of three cylinders

November-December 1990 73 Table 2. Concrete mix proportions and test data (5000 psi specified strength). were compared to the non-fly ash con­ Concrete supplier: Prestressed Concrete Plant No. 1. crete mixes from the same concrete plant). Mix No.2, which has 10 percent 2 3 4 5 6 Mix No. 1 fly ash replacement, showed strength Specified design increases of roughly 12 percent when strength, psi 5000 5000 5000 5000 5000 5000 compared to the strength results for the Cement, lbs 628 572 554 528 491 459 concrete without fly ash (Mix No. 1) at Fly ash, lbs 0 77 119 160 198 238 the various test ages (see Table 4). When the amount of fly ash replace­ Water, lbs* 283 263 253 248 237 227 ment was increased, the strength gain at Sand@ SSD, lbs 1278 1294 1328 1343 1332 1370 early age was more pronounced. For I in. aggregates @ example, Mix No.4, which has 20 per­ SSD, lbs 1807 1830 1877 1899 1884 1887 cent fly ash replacement, showed strength increases of around 50 percent W/(C +FA) 0.45 0.41 0.38 0.36 0.34 0.33 for the 19-hour, 22-hour, 3-day and 7- Slump, in. 2%t 6\12 6% 4% 7 4\14 day ages, when compared to the con­ Air content, percent 5.4 4.5 2.4 2.0 2.1 1.6 crete without fly ash (Table 4 ). Mix No. 6, which has the highest fly ash replace­ Air temperature, °F 70 70 70 70 70 70 ment, at 30 percent, had an even higher Concrete temperature, °F 69 66 70 69 69 69 strength gain at the 7 -day age, at 65 per­ Concrete density, pcf 148.0 149.5 153.0 154.7 153.4 154.9 cent. These results clearly indicate that * 90 fluid oz. of a nominal 42 percent solid sodium napthalene condensate ASTM C-494 Type F admixture Class C fly ash usage increased the (superplasticizer) was added to all mixes. early age strength of concrete. There­ t Reduced slump because of delay in testing; actual slump approximately 5 in. initially when truck arrived. 3 fore, this Class C fly ash can be used to Metric (SI) conversion factors: 145 psi= I MPa; I in.= 25.4 mm; I op = 1.8°C + 32; I cu yd = 0.7646 m ; 3 lib= 0.4536 kg; I pcf = 16.02 kg!m . produce high early strength concrete, in quantities of up to at least 30 percent cement replacement. Table 3. Concrete mix proportions and test data (5000 psi specified strength). For Mixes 8 to 12 (Table 5), strength Concrete supplier: Prestressed Concrete Plant No. 2. gain at early ages is also very good to Mix No. 7 8 9 10 11 12 excellent when compared to the con­ Specified design crete without fly ash (Mix No. 7). Mix strength, psi 5000 5000 5000 5000 5000 5000 No. 8, the 10 percent fly ash mix,

Cement,lbs 628 571 527 498 463 432 showed strength gains of around 17 percent at ages up to and including 7 Fly ash, lbs 0 76 Ill 149 185 222 days (Table 5). The strength gains were Water, lbs* 276 254 248 242 236 232 roughly the same for the rest of the mix­ tures, with a peak gain occurring for the Sand@ SSD, lbs 1357 1370 1338 1345 1333 1333 20 percent mixture (Mix No. 10). The I in. aggregates @ strength results indicate that cement re­ SSD, lbs 1783 1800 1758 1767 1752 1751 placement with up to 30 percent fly ash W/(C +FA) 0.44 0.39 0.39 0.37 0.36 0.35 increased the early age strength relative Slump, in. 8\12 8 8 6 7\12 8If.1 to the mixture without fly ash. There­ fore, fly ash can be used to produce Air content, percent 4.9 6.0 7.3 5.8 7.2 7.4 high early strength concrete for pre­ Air temperature, °F 71 78 78 71 71 71 cast/prestressed concrete applications. Concrete temperature, oF 84 86 86 87 87 85 Figs. 1 and 2 provide a more complete picture of the strength improvement for Concrete density, pcf 149.8 148.0 147.5 148.2 147.0 147.0 fly ash concrete mixtures when com­ 3 Metric (SI) conversion factors: 145 psi= I MPa; I in.= 25.4 mm; I op = 1.8°C + 32; I cu yd = 0.7646 m ; pared to concrete without fly ash. I lb = 0.4536 kg; I pcf = 16.02 kg!m3 Water Demand in laboratory work. Therefore, the data In general, the test results for these Figs. 3 and 4, associated with con­ has a little more variability than one two different plants followed a similar crete produced at Plant I and Plant 2, may be accustomed to seeing because it pattern. Mixes 1 and 7 are for the con­ respectively, show the relationship be­ is based on the average of two cylin­ crete without fly ash. Mixes 2 through 6 tween the percentage of fly ash replace­ ders. However, the data does show a are compared to Mix No. 1, while ment and the amount of water required pattern of increased strength develop­ Mixes 8 through 12 are compared to for the same workability. It is apparent ment with the use of the Class C fly ash. Mix No.7 (i.e., fly ash concrete mixes from these figures that as the amount of

74 PCIJOURNAL Table 4. Concrete strength test data (5000 psi specified strength). from both plants (Tables 2 and 3). Fig. Concrete supplier: Prestressed Concrete Plant No. 1. 5 reveals that as the amount of fly ash replacement increases, the water to ce­ Mix No. 1 2 3 4 5 6 mentitious material ratio decreases for Specified strength, psi 5000 5000 5000 5000 5000 5000 the same workability. This is indeed a Percent fly ash 0 10 15 20 25 30 well documented fact in the litera­ ture. s.IO.II,I3 Test Compressive strength, psi The data from this project confirm age, that fly ash concrete requires less water days Act. Avg. Act. Avg. Act. Avg. Act. Avg. Act. Avg. Act. Avg. for the same workability as a similar 19hours 2720 2950 3330 4170 3860 3110 concrete without fly ash. 22 hours 2790 3180 3750 4140 3400 3290 Workabi-lity 3 days 3040 3710 4100 4900 4900 4280 3235 -- 3800 -- 4095 -- 4890 - 5060 - 4475 3 days 3430 3890 4090 4880 5130 4670 Workability was observed and noted throughout the project. All the concrete 7 days 3860 4210 5590 5160 6510 6260 3750 f.-- 4155 -- 5520 -- 5640 -- 6315 1---- 6170 produced was homogeneous and cohe­ 7 days 3640 4100 5450 6120 6120 6080 sive. Therefore, it may be stated that the 14 days 4070 4740 6650 5910 7110 7110 fly ash replacement did not affect these 4210 1- 4685 1---- 6615 -- 6175 1---- 7075 1---- 7305 14 days 4350 4630 6580 6440 7040 7500 properties. Slump readings noted in Ta­ bles 2 and 3 show variations because of 28 days 4740 5270 7360 8450 8770 8520 4774 -- 5395 1---- 6830 -- 8080 -- 8435 -- 8365 the use of the superplasticizer. Other re­ 28 days 4810 5520 6300 7710 8100 8210 searchers6·7·8·13 have reported that fly

3 ash concrete improves workability, and Metric (SI) conversion factors: 145 psi= I MPa; I in.= 25.4 nun; I °F = 1.8°C + 32; I cu yd = 0.7646 m ; 3 lib= 0.4536 kg; I pcf = 16.02 kg/m . the data drawn from this project con­ firm this fact because even though the water to cementitious ratio decreased as Table 5. Concrete strength test data (5000 psi specified strength). the fly ash content was increased, Concrete supplier: Prestressed Concrete Plant No.2. clearly acceptable workability was Mix No. 7 8 9 10 11 12 maintained. Specified strength, psi 5000 5000 5000 5000 5000 5000 Percent fly ash 0 10 15 20 25 30 IMPLEMENTATION Since completion of this initial re-. Test Compressive strength, psi search program, Plant No. 1 has not yet age, days Act. Avg. Act. Avg. Act. Avg. Act. Avg. Act. Avg. Act. Avg. implemented its new mix proportions. However, Plant No. 2 has revised its 11hours 3180 3980 3900 4300 3580 3500 mixes for daily production. An equiva­ 13 hours 3980 4460 5090 4850 4140 3900 lent of 15 percent fly ash replacement 26 hours 5210 5730 6570 6330 5890 5850 mix (Mix No. 9) was selected. After some experience, management decided 3 days 5890 7160 7480 7240 6840 7080 to increase the fly ash replacement level 7 days 6680 7560 8280 8200 7600 7960 to 20 percent and eventually to 25 per­ 6445 1----- 7660 -- 8160 r-- 8180 -- 7640 e---- 7880 7 days 6210 7760 8040 8160 7680 7800 cent (Mix Nos. 10 and 11). To obtain 14 days 7120 8750 9030 8910 8590 9070 more consistent results throughout the 7020 1- 8810 1-- 8890 -- 8830 1---- 8535 -- 9070 year, including the winter months, the 14 days 6920 8870 8750 8750 8480 9070 plant is now using an equivalent of 20 28 days 8120 9670 10420 9510 9550 9830 percent fly ash replacement mixture 7820 -- 9610 1-- 10025 -- 9810 1--- 9530 -- 9880 28 days 7520 9550 9630 10110 9510 9930 (Mix No. 10) every day. In the past 15 77 days 8910 10400 10500 10070 10180 10400 months since the plants started using fly

3 ash, cement use has been reduced by Metric (SI) conversion factors: 145 psi= I MPa; I in.= 25.4 nun; I op = 1.8 °C + 32; I cu yd = 0.7646 m ; 3 about 5000 tons (4535 t) for a similar I lb = 0.4536 kg; I pcf = 16.02 kg/m . amount of production. The Plant No. 2 concrete is heated fly ash content increases the water de­ placement required only 229 lb ( 104 during the winter months to obtain a mand decreases, while maintaining ap­ kg) of water for the same workability. concrete placing temperature of about proximately the same workability. For Fig. 5 shows the relationship be­ 80°F (27°C). The initial concrete tem­ example, Mix No. 1 without fly ash re­ tween the water to cementitious materi­ perature during other times of the year quired 298 lb (135 kg) of water, while als ratio, by weight, and the percentage is maintained at about 65° to 70°F (18° Mix No.6 with 30 percent fly ash re- of fly ash replacement for the concretes to 21 °C). Before the plant started using

November-December 1990 75 the plant operator, the heating costs be­ 10 fore and after the use of fly ash has re­

9 mained the same.

8 ·- CONCLUSIONS "'Q_ The major conclusions which can be :i f--- drawn from this project about the use of (.!) ~ 6 z w v"' Class C fly ash are: 0: c f- 5 1. The test data indicate that replac­ U1 "'Vl :::J w 0 ing cement with up to 30 percent of a > L 4 ~ f--- lf) Class C fly ash increases early age lf) w strength when compared to concrete 0: KEY [W/CC+FAl]* ()_ L: 0 0% FLY ASH [ 0. 45] made with no fly ash. Therefore, con­ 0 2 10% FLY ASH [ 0. 41 ] u + crete mixtures with Class C fly ash can X 15% FLY ASH [ 0. 38] c::J 20% FLY ASH [ 0. 36] be used to produce high early strength 8 25% FLY ASH [ 0. 34] . 30% FLY ASH [0. 33] concrete for precast/prestressed con­ 0 crete products. 0 14 28 2. As the amount of fly ash incorpo­ AGE. days rated in concrete mixtures increases, the water required for the same work­ Fig. 1. Comparison of compressive strength vs. age for Plant No. 1 [5000 psi (34 MPa)]. Note: Corresponding slump and air content values are shown in Table 2. ability decreases. 3. Increasing fly ash replacement in concrete improves workability and thus allows a decrease in the water demand. 4. For the 0 to 30 percent fly ash re­ placements with the same workability, the water to cementitious ratio de­ creased significantly as the fly ash con­ tent increased. "'Q_ 5. The authors want to emphasize :i f--- the importance of performing trial mix­

(.!) ~ z tures with each source of fly ash. The w v"' 0: c f--- fly ash used in this study is a high qual­ lf) "' "':::J ity Class C fly ash and the mixture pro­ w 0 L ::: f--- portions shown here are for this specific lf) lf) fly ash. There is no substitute for trial w 0: KEY [W/CC+FA)]* ()_ mixes with the specific concrete mak­ L: 0 0% FLY ASH [ 0. 44 J 0 10% FLY ASH [ 0. 39 J u + ing ingredients. X 15% FLY ASH [ 0. 39] D 20% FLY ASH [ 0. 3 7 ] 8 25% FLY ASH [ 0. 36 J . 30% FLY ASH [ 0. 35 J RECOMMENDATIONS

0 14 28 Precast/prestressed concrete product suppliers not using Class C fly ash AGE, days should consider the advantages of using Fig. 2. Comparison of compressive strength vs. age for Plant No. 2 [5000 psi (34 this material in daily production. The MPa)]. Note: Corresponding slump and air content values are shown in Table 3. authors recommend starting with 20 percent cement replacement with fly ash (following successful trial mix­ fly ash, its preset time was 4 hours. hours total time from preset to cool­ tures), and after accumulating experi­ During this time the concrete tempera­ down. ence, gradually increasing the quantity ture was raised by about 5°F (2.8°C) After this plant started using fly ash to 30 percent. Several advantages are: per hour. Then, the concrete tempera­ in its daily production mixes, the total 1. Improved Economics - Im­ ture was raised to the desired level at time from preset to cool-down is still proved economics are possible as a re­ 20° to 30°F ( 11 to 17°C) per hour dur­ maintained at about 10 hours. The pre­ sult of reduced raw material costs re­ ing a 3-hour period and held at that tem­ set time has been increased from 4 to 5 sulting in the use of more competitive perature for an additional 2 hours. After hours, but the temperature raising and products over a wider geographical re­ this, the precast/prestressed concrete holding period has been decreased from gion. product is cooled down in a 1-hour time 5 to 4 hours. The 1-hour cool-down pe­ 2. Higher Quality - Class C fly ash period. Therefore, it took about 10 riod remains unchanged. According to usage in concrete provides higher qual-

76 PCI JOURNAL 300 ( ity products which include higher den­ sity with reduced permeability, in­ 290 - creased strength and other properties. "' ~ 280 - 3. Increased Productivity -Fly ash concrete mixes are handled more easily 0:: w 270 - f-- because of improved workability.

220 I I T T I Cement Content High Strength Con­ 0 I 0 20 crete,'J Cement and Concrete Research, Percent Cement Replacement by Fly Ash V.l7, 1987,pp.283-294. 2. Naik, T. R., and Ramme, B. W., "High Fig. 3. Relationship between percent cement replacement by fly ash and water Strength Concrete Containing Large demand for Plant No. 1. [Slump= 53/4 in.± 11;2 in. (146 mm ± 38 mm).] Quantities of Fly Ash," ACI Materials Journal, V. 86, No. 2, 1989, pp. 111- 116. 3. Naik, T. R., and Ramme, B. W., "Low 300 Cement Content High Strength Struc­ tural Grade Concrete With Fly Ash," 290- presented at the 1986 ACI Fall Conven­ ~"' 280 .., tion, in Baltimore, MD, November 1986. 0:: w 4. Naik, T. R., and Ramme, B. W., "Set­ f-- 270 - < 3 ting and Hardening of High Fly Ash u._ 260 Content Concrete," Proceedings, 0 ® American Coal Ash Utilization Sympo­ zf-- 250- :J sium, Washington, D.C., October 1987. ~ ® 5. Naik, T. R., and Ramme, B. W., "Ef­ - view," ACI Journal, Proceedings V. 72, (l) 0 Plant No. 2 0. 45 i~ s May 1975, pp. 225-232. f-- 9. Price, J. D., Troop, P., and Gershman, <( cr: H. W., "Potential for Energy Conserva­ Vl ® :::::> 0. 40 - tion Through the Use of Slag and Fly 0 0 ~ f-- Ash in Concrete," National Technical f--z Information Service, SAN -1699-T1, u..o >:: 0 u..o 0. 35 - 0 Distribution Category UC-951, De­ L) ® cember, 1978. 0 f-- 10. "Properties and Use of Fly Ash in Port­ cr: ® u..o f-- land Cement Concrete,'' Technical Re­ <( 0. 30 T T I I I 3 port CR-79-2, Tennessee Valley Au­ 0 I 0 20 30 40 thority, Knoxville, TN, February 1979. Percent Cement Replacement by Fly Ash 11. Berry, E. E., and Malhotra, V. M., "Fly Fig. 5. Relationship between percent cement replacement by fly ash and water to Ash for Use in Concrete -A Critical cementitious ratio for Plant No. 1 and Plant No. 2. See Tables 2 and 3 for Review,'' ACI Journal, Proceedings V. corresponding slump and air content values. 77, March-Aprill980, pp. 59-73.

November-December 1990 77 12. "Performance of Concrete in Marine 1983. 21. Albinger, J. A., "Fly Ash for Strength Environment," ACI Publication SP-65, 17. Cook, J. E., "Fly Ash in Concrete- and Economy," Concrete lnterna- Detroit, MI, 1980. Technical Considerations," Concrete tiona!, V. 6, No.4, Aprill984, pp. 32- 13. "Effects of Fly Ash Incorporation in International, V. 5, No. 9, September 34. Cement and Concrete," Proceedings, 1983, pp. 51-59. 22. Malhotra, V. M., "Use of Mineral Ad- Symposium N of the Materials Re- 18. Mehta, P. K., "Testing and Correlation mixtures for Specialized Concretes," search Society, November 1981. of Fly Ash Properties and Respect to Concrete International, V. 6, No. 4, 14. "Sulfate Resistance of Concrete," ACI Pozzolanic Behavior," EPRI CS-3314, Aprill984, pp. 19-24. Publication SP-77, Detroit, MI, 1982. Project 1260-26,January 1984. 23. Ravina, D., "Slump Loss of Fly Ash 15. "Fly Ash Concrete," Symposium Pa- 19. Hague, M. N., Langan, B. W., and Concrete," Concrete International, V. pers from the Denver Fly Ash Sympo- Ward, M. A., "High Fly Ash Con- 6, No.4, Aprill984, pp. 35-39. sium, Anaheim, CA, October 1983. cretes," ACI Journal, Proceedings V. 24. Malhotra, V. M., "Technology of Con- 16. Malhotra, V. M., "Fly Ash, Silica 81, January-February 1984, pp. 54-60. crete When Pozzolans, Slags and Fume, Slag and Other Mineral By- 20. "Publications List by the National Ash Chemical Admixtures Are Used," Pro- Products in Concrete," V. 1 and V. 2, Association," Washington, D.C., April ceedings, ACI-RILEM Joint Seminar, ACI Publication SP-79, Detroit, MI, 1984. Monterrey, N.L., Mexico, March 1985.

78 PCIJOURNAL