MICROSTRUCTURE AND SHRINKAGE BEHAVIOR OF MASSIVE CONCRETE CONTAINING PFBC COAL ASH

Transcription

1 8 - November 24, Barcelona, Spain MICROSTRUCTURE AND SHRINKAGE BEHAVIOR OF MASSIVE CONCRETE CONTAINING PFBC COAL ASH A. Nakashita (), S. Kondo (2), I. Maruyama (2) and R. Sato (2) () CHUGOKU ELECTRIC POWER CO., Inc. Technical Research Center, Japan (2) HIROSHIMA UNIVERSITY, Department of Civil and Environmental Engineering, Japan Abstract An experimental investigation is carried out on the effect of PFBC coal ash and high temperature on microstructure and shrinkage behavior of concrete containing PFBC coal ash (PFBC concrete). The major parameters adopted in the present study are concrete temperature at early age, water-to-binder ratios (W/B) and PFBC coal ash replacement ratios, respectively, in which the concrete temperature simulates that due to hydration heat generated in massive concrete. Experimental results showed that early-age strength of PFBC concrete until the age of 3 days was improved when W/B was.3, corresponding to microstructure which became denser as temperature rose. PFBC concrete showed compressive strength approximately similar to that of plain concrete under 6 and 8 independent of W/B except for the replacement ratio of 5%, while that showed the marked rate of increase even at the age of 365 days when W/B of.3 and exposed to 2. Effectiveness in reducing shrinkage strain and its induced stress due to self-desiccation was observed in PFBC concrete with W/B of.3 under 2. However, PFBC coal ash did not necessarily contribute to reducing long-term shrinkage and its induced stress except for the case of W/B of.3 under 2. Keywords: PFBC coal ash, Concrete, Microstructure, shrinkage, Long-term strength, Temperature effect. INTRODUCTION A pressurized fluidized bed combustion thermal power plant (PFBC) is a coal-fired thermal power plant especially developed for the enhancement of generating efficiency and the environmental load reduction. In the PFBC plant, coal is mixed with pulverized limestone for desulfurization. Compared with ordinary fly ash, the coal ash produced from this type of power plant (PFBC coal ash) is characterized to contain large amounts of CaO and SO 3, and small amounts of SiO 2. Moreover, the amounts of SiO 2 and SO 3 don t satisfy the limit values of SiO 2 for fly ash and SO 3 for blast-furnace slag specified by Japanese Industrial Standards (JIS), respectively. From this fact, PFBC concrete is expected to demonstrate rapid strength development compared with concrete containing ordinary fly ash []. Furthermore, the generation of ettringite as well as expansive hydrate of Ca(OH) 2 is expected to reducing shrinkage at early ages. On the other hand, PFBC concrete may have the possibility for losing strength stability due to large amounts of SO 3 [2] and for less development of long-term strength due to small amounts of SiO 2 resulting in pozzolanic reaction. 87

2 8 - November 24, Barcelona, Spain The purpose of this study is to investigate experimentally development of strength and shrinkage on PFBC concrete with time, relating to its microstructure. The major parameters adopted in the present study are concrete temperature at early age; 2, 6 and 8, W/B;.3 and.45 and PFBC coal ash replacement ratios;, 3 and 5%, respectively, in which the concrete temperature simulates that due to hydration heat generated in massive concrete. 2. OUTLINE OF EXPERIMENT 2. MATERIALS AND MIXTURE PROPORTIONS OF CONCRETE Table shows properties of materials used in making concrete specimens, and Table 2 shows chemical compositions and physical properties of normal portland cement, PFBC coal ash, conventional fly ash, and specified values of JIS. Table 3 shows mixture proportions of concrete in which there are two levels of W/B: one of.45 and the other of.3. So, the replacement ratios of PFBC coal ash for total mass of binder were adjusted to be 3% and 5%. The unit contents of water and coarse aggregate were designed to be 65kg/m 3 and 989kg/m 3 for all types of concrete, respectively. The target values of flow slump and air content are listed in Table 4. They were controlled by the dosage of the superplasticizer and the air-entraining agent. Kinds Normal Portland Cement PFBC Coal Ash Fly Ash Blast- Furnace Slag Table : Properties of Materials of Concrete Materials Kinds Properties Cement (C) Normal Portland Cement Density:3.6g/cm 3,Blaine Fineness: 338cm 2 /g Supplementtary Cementitious Materal PFBC Coal Ash Density:2.6g/cm 3,Blaine Fineness: 458cm 2 /g Fine Aggregate Density:2.6g/cm 3,Water Absorption:.78%, River Sand (S) Fineness Modulus: 2.9 Coarse Density: 2.62g/cm 3, Water Absorption:.88%, Crushed Stone Aggregate(G) Fineness Modulus: 6.8, Maximum size: 2mm Chemical Superplasticizer (SP) Density:.5 g/cm 3 Admixture Air Entraining Agent (AE) Density:.3 g/cm 3 Table 2: Chemical Compositions and Physical Properties of Binders Chemical Compositions (%) ig.loss SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO SO 3 Na 2 O K 2 O ( 3.) Water Content (%) Physical Properties Flow Value (%) M.B. Absorption (mg/g) ( 5.).3 ( 3.) 73.8 ( 45) (JIS); Specified values of JIS W/B* (%). ( 4.)..2 Table 3: Mixture Proportions of Concrete s/a (%) PFBC/B (%) Unit Content (kg/m 3 ) --- (.) --- (.) 2 ( 95) Chemical Admixture.59 ( 9) --- Symbol B SP AE W S G (B %) (B %) C PFBC 3-P P P P P *B=C+PFBC 872

3 8 - November 24, Barcelona, Spain Table 4 : Target value of flow slump and air content W/B.3.45 Flow slump(cm) Air content (%) TEMPERATURE HISTORY OF SPECIMEN In order to investigate the effects of temperature increases at young ages on strength development and shrinkage behavior the temperature history of the specimens is shown in Figure. This pattern of rise in temperatures modeled mass concrete. Specimens were covered with polyethylene films and wet fabrics just after casting followed by finishing, and then were exposed in a room in which temperature and relative humidity were kept constant at 2 and 6 5%, respectively for.5 or.63 days. All specimens were de-molded and sealed with aluminum foil adhesive tape to prevent water evaporation and absorption just after curing. Casting.63 Rate of temperature rise :3 /hr Rate of temperature descent :3 /hr Age(days) demolded and sealed 2,6% R.H.(curing 9 % R.H.(climate chamber) removal sealing,in the air 2,6% R.H.(curing room) Figure : Temperature history of specimens As is shown in Figure, sealed specimens were heated in a computer-controlled climate chamber to 6 and 8, with a temperature rise of 3 /hr, and were exposed to the final temperatures for three days, then, the temperatures were lowered at a likewise rate to 2. Relative humidity for the high temperatures for the three days was from 9% to % in the above chamber. Specimens were stored in the same chamber for seven days then, were stored in the above- mentioned curing room after the tape on the specimens was removed. 2.3 PREPARTION OF SPECIMENS AND METHOD OF EXPERIMENTS Experiments on autogenous shrinkage as well as total shrinkage and drying shrinkage were carried out. Quadratic prisms made in horizontal formworks of by -mm in cross section and 4-mm in length were used for the tests. Shrinkage strain was measured by means of strain gauge embedded in the above specimens along with thermocouples. Additionally, in order to decrease the friction between the concrete and formwork as small as possible, Teflon sheets of -mm in thickness were placed inside the steel formwork before casting. Furthermore, in order to free concrete expansion due to hydration heat of cement and supplementary cementitious material from restraint at both ends, foamed polystyrene sheets of 2-mm in thickness were placed between the polystyrene films and the formwork. The outline of the formwork and specimen is shown in Figure 2. In this study, the thermal expansion coefficient of concrete assumed that it was constant in -6 / immediately after casting. And shrinkage strains of all specimens were obtained based on above-mentioned condition. Restrained stress test was carried out, as is illustrated in Figure 3, according to Test Method for Autogenous Shrinkage Stress of Concrete, which was recommended by Technical Committee on Autogenous Shrinkage of Concrete of The Japan Concrete Institute 873

4 8 - November 24, Barcelona, Spain [3]. The ratio of cross sectional area of restraining steel to that of the pure concrete was 2.8%. The preparation of specimens and measurement of compressive strength were carried out according to JIS A 32 and JIS A 8. Shape and size of specimens of used for compressive strength measurement was by 2-mm cylinder. The test ages of specimens were, 3, 7, 28, 9 and 365 days. Mortar pieces were obtained from concrete specimens after compressive strength testing to measure pore size distribution by means of a mercury intrusion porosimeter. Strain Gauge Coating Concrete Formwork Wrap film Foamed polystyrene sheet Seal(aluminum foil adhesive tape) 9mm Urethane insulation CL Teflon sheet Embedded gauge Polyester film Figure 2: Outline of specimen for shrinkage test Reinforcement ;D9 Specimen mm mm Figure 3: Outline of specimen for restrained stress test 3. EXPERIMENTAL RESULTS AND DISCUSSION 3. Compressive strength The influence of the temperature as well as that of replacement ratios of PFBC coal ash of % (P), 3% (P3) and 5% (P5) on a logarithmic plot compressive strength timedevelopment of concrete specimens with W/B of.3 and.45 is shown in Figure 4. In addition, Figure 5 shows in a logarithmic plot compressive strength ratio time-development of the concrete specimens with W/B of.3 and.45. Here, compressive strength ratio is defined by compressive strength of PFBC concrete divided by that of plain concrete (P), Compressive Strength (N/mm 2 ) C 6 C 8 C 4 3-P 3-P P 45-P3 45-P Age day Figure 4: Relationship between Compressive strength and Ages Compressive strength ratio.5 2 C 6 C 8 C.5 3-P3/3-P 45-P3/45-P 45-P5/45-P Age(day) Figure 5: Relationship between Compressive strength ratio and Ages 874

5 8 - November 24, Barcelona, Spain which is exposed to the same temperature. As for the case of 2, the compressive strength of P3 was smaller than that of P until the age of 28days, while P3 exceeded P at and after 9days in case of W/B of.3. In this connection, strength development of P3 showed the marked rate of increase even at the age of 365days. On the other hand, the compressive strength decrease corresponding to the PFBC coal ash replacement ratio increases in case of W/B of.45. The compressive strength of P3 almost became equal with P in age of year, while the compressive strength of P5 was 3% lower than that of P. As for the case of 6, a difference in strength of P and P3 became small compared with 2, and P3 was equal to P after 28days in case of W/B of.3. On the other hand, the specimens with W/B of.45 showed that the compressive strength decrease with the PFBC coal ash replacement ratio increases as well as 2. Similar to the case of 2, the compressive strength of P5 was also 3% lower than that of P, and P3 reached almost the same strength as P at year. As for the case of 8, the compressive strength of P3 specimens with W/B of.3 became it more than the equal to that of P at and after the age 3days. However, in case of W/B of.45, the compressive strength of P3 was nearly % lower than that of P until the age of 9 day, and reached the same strength as P at year as well as 2 and 6. From above-mentioned results, it has been observed that early-age strength of PFBC concrete until the age of 3 days improved corresponding to rise in temperature in case of W/B of.3. However, long-term strength of PFBC concrete developed approximately similar to that of plain concrete under 6 and 8 independent of W/B except in Shrinkage strain In this study, unsealed specimens were exposed to drying from the age of 7 days after all specimens under sealing were exposed at 2, 6, and 8, respectively. Figure 6 show in a logarithmic plot the shrinkage strain time-development of P and P3 specimens with W/B of.3 (Figure 6 (a)) and P, P3 and P5 specimens with W/B of.45 (Figure 6 (b)) in (a) W/B=.3 Shrinkage strain W/B=.3, Age day (b) W/B= High Temperature P -4 P3-5 P5-6 W/B=.45,2 W/B=.45, Age day Figure 6: Relationship between Shrinkage strain and Ages Shrinkage strain( -6 ) High Temperature P P3 High Temperature W/B=.3,6 W/B=.3,

6 8 - November 24, Barcelona, Spain Table 5 : Shrinkage strain results (W/B=.3) Temperature Strain PFBC coal ash replacement ratio -6 P P3 P5 a d T a d T a d T Table 6 : Shrinkage strain results (W/B=.45) Strain PFBC coal ash replacement ratio Temperature -6 P P3 P5 a d T a d T a :Autogenous shrinkage strain until the age of 7days d :Drying shrinkage strain at the age of 4days T :Total shrinkage strain at the age of 4days each temperature. Furthermore, in Table 5 and 6, Autogenous shrinkage strains until the age of 7 days, Drying shrinkage strains and Total shrinkage strains at the age of 4 days are summarized, respectively. As for the case of 2, autogenous shrinkage strains until the age of 7 days of P3 with W/B of.3 has been decreased significantly to about 5% of P (see Figure 6 (a), Table 5). However, in case of 6 and 8, autogenous shrinkage strains of P3 became slightly large compared with that of P. On the other hand, as for W/B of.45, autogenous shrinkage strains has a tendency to became slightly small corresponding to the PFBC coal ash replacement ratio increase in case of 2 as well as W/B of.3 (see Figure 6 (b), Table 6). One of the reasons for these results might be the contribution of the production of ettringite due to originate in the chemical composition of PFBC coal ash [4] that is an expansive hydrate. In the case of 6, the difference in autogenous shrinkage strains of PFBC concrete and plain concrete was small, and the contribution of PFBC coal ash to reducing autogenous shrinkage was not observed clearly as well as W/B of.3. The total shrinkage strain of P3 with W/B of.3, i.e. the sum of autogenous shrinkage and drying shrinkage at the age of 4 days in each temperature showed that become small compared with that of P, while the difference in the total shrinkage strain of P and P3 was small. On the other hand, as for W/B of.45, the total shrinkage strains also has been decreased corresponding to the PFBC coal ash replacement ratio increase in case of 2, while it has been increased in case of 6 (see also Table 6). As a result of the above analysis, the shrinkage strain of PFBC concrete with W/B of.3 showed the tendency to become small obviously as PFBC coal ash replacement ratio increase in case of 2, whereas the reduction effect of that by PFBC coal ash was not observed definitely in case of high-temperature regardless W/B. Moreover, the shrinkage strain of unrestraint specimens have the tendency to increase greatly as temperature rises in each PFBC coal ash replacement ratio and W/B, while the shrinkage strain has the tendency to decrease greatly as temperature falls (see also Figure 6). It is thought that the shrinkage strain of unrestraint specimen having shown such behavior in the high-temperature relates to the time dependency of a concrete thermal expansion coefficient with progress of hydration at early ages. 3.3 Restrained stress In this study, it was assumed that the thermal expansion coefficient of concrete and the reinforcement was equal, and restrained stress obtained from the strain of the reinforcement. Figure 7 show in a logarithmic plot the restrained stress time-development of the P and P3 specimens with W/B of.3 (Figure 7 (a)) and P, P3 and P5 specimens with W/B of.45 (Figure 7 (b)) in each temperature. Furthermore, in Table 7 and 8, Autogenous shrinkage stress until the age of 7 days, Drying shrinkage stress and Total shrinkage stress at the age of 4 days are summarized, respectively. 876

7 8 - November 24, Barcelona, Spain As is shown in the Figure 6 (a), the autogenous shrinkage stress of P3 specimen with W/B of.3 became small in each temperature compared with that of P. In case of 2, P3 has been decreased obviously to about 5% of P as well as the autogenous shrinkage strains. However, in case of 6, the difference in autogenous shrinkage strain of P and P3 has been decreased (see Table 7). Similar to the case of W/B of.3, the autogenous shrinkage stress of specimen for W/B of.45 also has been decreased corresponding to the PFBC coal ash replacement ratio increase in each temperature, while the difference in autogenous shrinkage strain of PFBC concrete and plain concrete was small in each temperature (see Figure 7 (b), Table 8). According to the Figure 6 (a), the total shrinkage stress at the age of 4 days of P3 specimen for W/B of.3 smaller than that of P in case of 2, while P3 was almost equal to P in case of 6. On the other hand, in the case of W/B of.45, the difference in the total shrinkage stress of P and P3 was small, and P5 was 5% smaller than P in case of 2. As for case of 6, P3 were larger obviously than P, and P5 was almost equal to P. From the above discussion of the factors affecting the restrained stress, it is observed that autogenous shrinkage stress of PFBC concrete with W/B of.3 decreased obviously in case of 2. On the other hand, effectiveness in reducing of PFBC coal ash in these shrinkage stress was not observed definitely in case of 6 regardless of W/B (see also Table 7, 8). Similar to the case of the shrinkage strain of unrestraint specimen, restrained stress has the tendency to increase greatly as temperature rises in each PFBC coal ash replacement ratio and W/B, while the stress has the tendency to decrease greatly as temperature falls (see also Figure 7). These facts imply that the thermal expansion coefficient of concrete at early ages is different from that of reinforcement. In consequence, the possibility that the thermal stress has tension tension Restrained stress(n/mm 2 ) Restrained stress(n/mm 2 ) (a) W/B= W/B=.3,2 P W/B=.3,6 2. P3.5 High Temperature Age(day) (b) W/B= W/B=.45,2 W/B=.45, P P3 P5 5 5 High Temperature Age(day) Figure 7: Relationship between Restrauned stress and Ages Table 7 : Restrained stress results (W/B=.3) Stress PFBC coal ash replacement ratio Temperature N/mm 2 P P3 P5 a d T a d T a :Autogenous shrinkage stress until the age of 7days d :Drying shrinkage stress at the age of 4days T :Total shrinkage stress at the age of 4days Table 8 : Restrained stress results (W/B=.45) Stress PFBC coal ash replacement ratio Temperature N/mm 2 P P3 P5 a d T a d T

8 8 - November 24, Barcelona, Spain been generated as above-mentioned behavior is considered. 3.4 Microstructure Relationship between microstructure and shrinkage The influence of the temperature as well as that of replacement ratios of PFBC coal ash of % (P) and 3% (P3) on cumulative pore volume of mortar specimens with W/B of.3 at the ages of 3, 28, and 365 days is shown in Figure 8. Furthermore, this figure show that the cumulative pore volume is divided into four ranges of pore size:.3 to.5 m,.5 to.5 m,.5 to 5. m and 5. to 34 m, respectively. In case of 2, cumulative pore volume of P3 specimen for W/B of.3 is slightly larger compared with that of P specimen at each age, while the cumulative pore volumes of P and P3 hardly decrease after the age of 28 days. Contribution of PFBC coal ash to reducing autogenous shrinkage, as is shown in Figure 6, is difficult to be explained by the pore volume with the diameter below 5nm [5], because the difference of pore volume below 5nm between PFBC concrete and plain concrete is not significant. In case of 6, PFBC concrete shows slightly larger cumulative pore volume than that of P and time-dependent decrease of the volume like the case of P from macroscopic point of view. This results differs from the case under 8 in which the difference between P3 and P for the cumulative pore volumes is negligible and no decrease of the volume with time is observed. However, the pore volumes with the diameter below 5nm of PFBC concrete obviously dominant more than that of plain concrete under 8 which is observed in the case under 6. Namely, above-mentioned pore volume increased in high-temperature that is Cumulative pore volume (ml/g) Cumulative pore volume (ml/g).3-.5 m.5-.5 m m.6 W/B= days 28-days 365-days 3-days 28-days 365-days 3-days 28-days 365-days.2 2 C 6 C 8 C P P P P P P P P P P3 P3 P3 P3 P3 P3 P3 P3 P3 PFBC coal ash replacement ratio Figure 8 : Cumulative pore volume of mortar specimens (W/B=.3) days 28-days 365-days P P3 P m.5-.5 m m 2 C P P3 P5 P P3 P5 3-days P P5 P3 W/B= days 365-days 6 C P P5 P P5 P3 P3 3-days 28-days 365-days 8 C P P P P3 P3 P3 PFBC coal ash replacement ratio Figure 9 : Cumulative pore volume of mortar specimens (W/B=.45) 878

9 8 - November 24, Barcelona, Spain assumed to be increasing shrinkage strain. It was assumed from the above findings that effectiveness in reducing shrinkage strain of PFBC coal ash might tend to decrease under high-temperature. Similar to the case of W/B ratio.3, the influence of the curing temperature as well as that of replacement ratios of PFBC coal ash of % (P), 3% (P3) and 5% (P5) on cumulative pore volume of mortar specimens with W/B of.45 at the ages of 3, 28 and 365 days is shown in Figure 9. Comparing roughly the results in Figure 8 with that in Figure 9, needless to say, cumulative pore volume of concrete with W/B of.45 is larger than that with W/B of.3. According to Figure 9, the cumulative pore volume becomes larger as the PFBC coal ash replacement ratio increases. This tendency is the most remarkable in case of 2 and becomes weaker as temperature rises and finally vanishes under 8. As for the pore volume which has the diameter smaller than 5nm, influence of PFBC coal ash replacement ratio on the volume with the same diameter is scarcely seen at the age of 3 days under 2, while dependence of the replacement ratio on that is observed, namely, P<P3<P5 in the pore volume under 6 at the age of 3 days. Effectiveness of PFBC coal ash in the reduction of autogenous shrinkage is not noticeable under both 2 and 6 while this ash slightly contributed to decrease the shrinkage compared with plain concrete, which should be due to the fact that water was not provided. One of the reason why there is no dependence of autogenous shrinkage on the pore volume with the diameter smaller than 5nm should be owing to the production of expansive hydrate such as ettringite and Ca(OH) 2. Similar to the case of autogenous shrinkage, it is difficult to explain drying shrinkage from viewpoint of pore volume, which has the diameter smaller than 5nm. Relationship between pore volume of >5nm in diameter and compressive strength Dependence of compressive strength on pore volume of >5nm in diameter is shown in Figure, relating temperature as well as that of replacement ratios of PFBC coal ash. As for the strength development of P3 specimen with W/B of.3, the cumulative pore volume of P3 at the age of 3 days decreased as temperature rose and became denser, and the strength of P3 was improved by the high-temperature. The reason for this is that pore volume of 5nm (.5µm) or larger which are considered to have a close correlation with the strength of concrete [6], decreased (see Figure (a)). On the other hand, as for the pore volume of the specimen with P3 after the age of 28days, the pore volume of 5nm (.5µm) or larger decreased at high-temperature and became Compressiv Strength (N/mm 2 ) W/B= (a) W/B=.3 3-days Compressive Strength P P3 28-days Pore volume P P3 365-days Temperature ( )..5 Pore volume of >5nm in diameter (ml/g) Compressiv Strength (N/mm 2 ) W/B= days (b) W/B=.45 Compressive Strength P P3 P5 28-days Pore volume P P3 P5 365-days Temperature ( )..5 Pore volume of >5nm in diameter (ml/g) Figure : Relationship between Pore volume of >5nm in diameter and compressive strength 879

10 8 - November 24, Barcelona, Spain denser compared with P. However, the less porous internal-structure of P3 in long-term age made no contribution to strength increase (see also Figure (a)). As for the case of W/B of.45, it did not necessarily agree to this more dense internalstructure and strength development though the pore volume of P3 and P5 specimens at each age decreased with temperature rising from 2 to 8 and became denser (see Figure (b)). It is necessary to clarify the mechanism of long-term strength development of PFBC concrete from chemical point of view. 4. CONCLUSIONS The conclusions obtained in this study are described below. Early-age strength of PFBC concrete until the age of 3 days was improved when W/B was.3, corresponding to microstructure which became denser as temperature rose. Long-term strength of PFBC concrete developed approximately similar to that of plain concrete under 6 and 8 independent of W/B except for the replacement ratio of 5%, while that showed the marked rate of increase even at the age of 365 days when the W/B of.3 and exposed to 2. Effectiveness in reducing shrinkage strain and its induced stress due to self-desiccation was observed in PFBC concrete with W/B of.3 under 2. However, PFBC coal ash did not necessarily contribute to reducing long-term shrinkage and its induced stress except for the case of W/B of.3 under 2. REFERENCES [] K. Kawai, Y. Yang, R. Sato, and T. Saitoh, 'Strength development of concrete mixed with PFBC ash (in Japanese)', Proceedings of the Japan Concrete Institute Vol.24, No., (22) [2] H. Sa-saki, N. Shintani, T. Kita, and K. Hukudome, 'Utilization of Coal ash Produced from Pressurized Fluidized Bed Combustion Thermal Power Plant for Concrete Additives (in Japanese)', Proceedings of the Japan Concrete Institute Vol.9, No., (997) [3] Japan Concrete Institute, 'Report of Autogenous shrinkage research committee', (996) 4-4,99-2. [4] A. Nakashita, S. Kondo, M. Tanaka and R. Sato, 'Strength Development of Concrete containing PFBC coal Ash Cured Under Elevated Temperature (in Japanese)', Proceedings of the Japan Concrete Institute Vol.25, No., (23) [5] P. Kumar Mehta, Paulo J.M. Monteiro, 'CONCRETE: Microstructure, Properties, and Materials', 2nd Edn (McGrow-Hill Co., Inc.), U.S.A., (985) [6] H. Uchikawa, Advances in Cement Manufacture and Use, 'Engineering Foundation Conference', Potosi, Missouri, (988)