This study investigated the effect of cement/wood ratios and wood storage conditions on hydration temperature, hydration time, and compressive strength of wood-cement mixtures made from six wood species: southern pine, white oak, southern red oak, yellow-poplar, sweetgum, and hickory. Cement/wood ratios varied from 13/1 to 4/1. Wood storage conditions consisted of air-dried and cold-stored wood. Results indicate that hydration temperature was drastically reduced, hydration time was prolonged, and compressive strength was reduced as cement/wood ratio was decreased. This effect was more pronounced for hardwood species and at lower cement/wood ratios. Cold storage of wood slightly increased hydration temperature and shortened hydration time of white oak and sweetgum but did not have any beneficial effect on the other four species. Results also indicate that mixtures with high cement/wood ratios used traditionally in laboratory for research purposes may not truly reflect the wood-cement compatibility at lower cement/wood ratios used in commercial production

Hong, Zhongli

Hse, Chung Y.

Lee, Andy W. C.

Phillips, Douglas R.

English

Wood and Fiber Science (E-Journal)

EFFECT OF CEMENT/WOOD RATIOS AND WOOD STORAGE CONDITIONS ON HYDRATION TEMPERATURE, HYDRATION TIME, AND COMPRESSIVE STRENGTH OF WOOD-CEMENT MIXTURES Andy W. C. Lee and Zhongli Hong Associate Professor and Research Associate Department of Forestry, Clemson University Clemson, SC 29634-1003 Douglas R. Phillips Project Leader S.E. Forest Expt. Station USDA, Forest Service Clemson, SC 29634 and Chung Y. Hse Principal Wood Scientist Southern Forest Expt. Station USDA, Forest Service Pineville, LA 7 1360 (Received May 1986) ABSTRACT This study investigated the effect of cement/wood ratios and wood storage conditions on hydration temperature, hydration time, and compressive strength of wood-cement mixtures made from six wood species: southern pine, white oak, southern red oak, yellow-poplar, sweetgum, and hickory. Cement/ wood ratios varied from 13/1 to 4/1. Wood storage conditions consisted of air-dried and cold-stored wood. Results indicate that hydration temperature was drastically reduced, hydration time was pro- longed, and compressive strength was reduced as cement/wood ratio was decreased. This effect was more pronounced for hardwood species and at lower cement/wood ratios. Cold storage ofwood slightly increased hydration temperature and shortened hydration time of white oak and sweetgum but did not have any beneficial effect on the other four species. Results also indicate that mixtures with high cement/wood ratios used traditionally in laboratory for research purposes may not truly reflect the wood-cement compatibility at lower cement/wood ratios used in commercial production. Keywords: Cement/wood ratio, air-dried and cold-stored wood, southern pine, white oak, southern red oak, yellow-poplar, sweetgum, hickory, hydration temperature, hydration time, compressive strength, Portland cement, calcium chloride, cylindrical compression sample. INTRODUCTION Mineral-bonded wood products were initially developed in Europe nearly half a century ago. The first product was magnesite-bonded light-weight wood wool (excelsior) board, which was later modified to adopt Portland cement as a binder. Currently, cement-bonded excelsior boards are produced in the United States and some other countries for roof decking and wall paneling applications. This product Wood and k't;rhe,- 9 , e n w .  19(1). 1987. pp. 262-268 (c) 1987 by the Sorlcty of Wood Science and Technolog> Lee et a/.-EFFECT OF CEMENT/WOOD RATIOS 263 TABLE 1 .  Maximum hydration temperature (OC) of 6 wood-cement mixtures at 4 dtferent cement/ wood ratlos.' Cement/wood ratio Soecles 13/1 10/1 7/1 5 /  1 4/ 1 Southern pine Air-dried 66.8 61.1 54.0 43.4 38.7 Cold-stored 66.7 60.9 53.4 45.0 38.4 White oak Air-dried 61.7 55.9 44.0 35.0 30.9 Cold-stored 66.7 61.0 52.5 40.8 30.1 Red oak Air-dried 64.2 56.7 44.9 32.5 26.7 Cold-stored 65.9 55.1 46.0 30.0 - 2 Yellow-poplar Air-dried 65.0 56.7 44.8 35.0 - Cold-stored 65.0 55.9 43.4 30.0 - Sweetgum Air-dried 63.4 55.0 42.5 26.7 - Cold-stored 65.9 57.6 48.4 36.0 - Hickory Air-dried 59.3 52.6 39.2 30.9 - Cold-stored 62.5 54.1 39.2 28.4 - I Each value IS  thc average of 3 samples. ' - designates that temperature d ~ d  not rlse above room temperature of 25 C within 96 hours of observation. has good acoustic and fire resistance properties, but its strength and thermal insulation capabilities are only moderate (Lee 1984, 1985). In the early 1950s, an American firm (Elmendorf, Inc. 1954) obtained several patents on cement-bonded wood particleboard which was made from wood par- ticles, planer shavings, and cement. The density and strength of this product were very high in comparison with excelsior board. Its resistance to fire, fungi, weath- ering, and its dimensional stability were excellent. Since that time, researchers have attempted to identify suitable wood species and select effective additives and treatments to improve this product (Biblis and Lo 1968; Liu and Moslemi 1985; Moslemi et al. 1983; Moslemi and Lim 1984). Past research on wood-cement compatibility has typically been camed out in the laboratory using mixtures with high cement/wood ratio of 13.3/1 (Weatherwax 1964, 1967). This ratio is far above that used in commercial production, and the high cement/wood ratio can overshadow the effect of species and treatments on hydration characteristics, especially when an effective additive is added to the mixture (Lee and Hong 1986). The purpose of this study was to investigate the effect of cement/wood ratios on hydration temperature, hydration time, and com- pressive strength of wood-cement mixtures. MATERIALS AND METHODS Six species of wood tested in this study were: southern pine (loblolly pine), white oak, southern red oak, yellow-poplar, sweetgum, and hickory. Two trees from each species, approximately 9 inches in diameter at breast height, were felled, debarked, and cut into bolts 24 inches in length. One half of the bolts were sawn into 1 -inch-thick boards and air-dried in the summer for 2 months. Planer shavings produced from these boards were refined in a Wiley mill so that only the material passing through a 20-mesh screen and remaining on a 40-mesh screen 264 WOOD AND FIBER SCIENCE, JULY 1987, V. 19(3) TABLE 2. Time (h) required to reach maximtun temperature of 6 wood-cement mixtures at 5 dzferent cement/wood ratios.' Cement/wood ratio Spcc~es 1311 1011 71 1 51 1 4/ 1 Southern pine Air-dried Cold-stored White oak Air-dried Cold-stored Red oak Air-dried Cold-stored Sweetgum Air-dried Cold-stored Hickory Air-dried Cold-stored I Each value 1s the average of  3 samples. - des~gnates that temperature dld not rise above room temperature of  25 C w ~ t h ~ n  96 hours of observation was used in this experiment. The other half of the bolts were stored in a cooler at a temperature of approximately 45 F for 2 months to simulate the winter storage condition in the southern USA. The cold-stored bolts were then sawn and reduced to shavings in the same manner as the air-dried wood. Type I Portland cement (500 grams) and an appropriate amount of wood shav- ings were weighed to constitute the following cement/wood ratios (oven-dry weight basis): 13/ 1, 10/ 1, 7/ 1, 5 /  1, and 4/ 1. The amount of water used for mixing was TABLE 3. Compresszve strength (psi) at 14 days curing age o f 6  wood-cement mixtures at dzfferent cernent/wood ratios. Cement/wood ratio Southern pine Air-dried 3,332 2,552 1,732 954 69 1 Cold-stored 3,666 2,844 1,873 934 647 White oak Air-dried 4,329 3,528 2,154 1,106 709 Cold-stored 4,340 3,332 2,122 1,044 614 Red oak Air-dried 4,239 3,332 2,032 1,094 459 Cold-stored 4,5 15 3,236 1,93 1 836 - 2 Sweetgum Air-dried 3,650 2,801 1,594 764 - Cold-stored 3,830 2,844 1,798 912 - Hickory Air-dried 4,36 1 3,507 1,693 1,120 - Cold-stored 4,653 3,629 1,367 546 - I Each value is the average o f  3 samples. ' Compress~on test was not conducted. Lee et a/.-EFFECT OF CEMENT/WOOD RATIOS CEMENTIWOOD RAT1 0 FIG. 1. Density of compression samples made of cement-wood mixtures at various cement/wood ratios. 2.7 milliliters per gram of wood (oven-dry basis) and 0.25 milliliter per gram of cement (Weatherwax 1964, 1967). Water came from 3 different sources: water in the wood, water in the calcium chloride solution, and added water. Three percent solid content calcium chloride (based on cement weight) in liquid form was added to each mixture. Since calcium chloride has been proven to be an effective and economical accelerator for cement hydration, it has been adopted widely in the wood-cement board industry. The wood-cement mixture was then tamped into a cylinder mold, and one cylindrical compression sample was made (ASTM 1983). From the remaining mixture, 350 grams were placed in a styrofoam cup, which was then placed in a 2-quart thermal jar for hydration time and temperature measurements (Lee and Hong 1986). The sample was kept in the mold without pressure for 24 hours or until its respective temperature sample reached the maximum temperature, which- ever was longer. Temperature recording was discontinued if no change was ob- served in 4 days. After the removal of the compression sample from the mold, it was placed in a conditioning chamber at 25 C and 50% relative humidity for curing. The sample was later tested in compression at the age of 14 days, and compressive strength was calculated from maximum load and cross-sectional area of sample. Each test for hydration and strength was repeated 3 times. RESULTS AND DISCUSSION Maximum hydration temperatures of wood-cement mixtures, including 6 species at 5 cement/wood ratios, are listed in Table 1. Without exception, hydration WOOD AND FIBER SCIENCE, JULY 1987, V. 19(3) TIME(t)  RE(IUIRED TO REACH MAX. TEMP.. Hr FIG. 2. Relationships between maximum hydration temperature and time required to reach max- imum temperature of wood-cement mixtures (combined data from air-dried and cold-stored wood). temperatures were drastically reduced when cement/wood ratios were decreased. Temperature reduction was due to the increase of wood (an inhibitory material) and the decrease of cement (a bonding and heat generating material), coupled with the reduced amount of calcium chloride. This reduction was greater for hardwood species than for southern pine. At cement/wood ratio of 4/1, yellow- poplar, sweetgum, and hickory did not reach a hydration temperature above 25 C (room temperature), while southern pine, white oak, and air-dried red oak did rise above room temperature. Cold storage of wood slightly improved the hydra- tion temperatures of white oak and sweetgum, but did not significantly affect the hydration temperatures of the other four species. Hydration time (time required to reach maximum hydration temperature) was drastically prolonged as cement/wood ratios were decreased, especially for hard- wood species (Table 2). At cement/wood ratio of 4/ 1, all hardwood species failed to gain temperature within 96 hours, except white oak and air-dried red oak. Cold storage of wood generally prolonged the hydration time, but white oak and sweet- gum had much shorter hydration times when the wood was cold-stored. Significant differences in hydration times between southern pine and hardwood species, at lower cement/wood ratios, indicate that hardwood species will require different processing techniques when used as raw materials for wood-cement board. As shown in Fig. 1, density of the compression sample is linearly proportional to the cement/wood ratio. Wood species has very little effect on the density of wood-cement mixture. Compressive strengths of wood-cement mixtures were expressed in pounds per square inch (psi) and are listed in Table 3. Compressive strengths of wood-cement mixtures were significantly reduced as cement/wood ratios were decreased. This can be attributed to the reduced density. Despite the lower hydration temperature and longer hydration time, most mixtures with hard- wood species had equal or higher compressive strength than southern pine at 14 days' curing age. For instance, at cement/wood ratio of 5/  1, white oak and some air-dried hardwood species (red oak, yellow-poplar, and hickory) had greater strength than southern pine. However, at cement/wood ratio of 4/1, only air- Lee et a1.-EFFECT OF CEMENT/WOOD RATIOS 267 TABLE 4. Percentage changes of maximum hydration temperature, hydration time, and compressive strength of wood-cement mixtures for each one part decrease in cernent/wood ratios (combined data from air-dried and cold-stored wood). CemenVwood ratlo ranges Soecics 13/1-10/1 loll-711 7/1-5/1 5/1-4/1 Maximum hydration temperature change (%) Southern pine 2 . 9  -4.0 -8.9 -12.8 Hardwoods -4.2 6 . 9  - 13.5 -20.5 Hydration time change (O/o) Southern pine 7.7 8.9 18.3 39.5 Hardwoods 19.6 34.1 59.3 62.3 Compressive strength change (O/o) Southern pine -7.7 1 1 . 1  -23.8 2 9 . 2  Hardwoods 8 . 0  -15.7 -23.8 -44.1 dried white oak had strength equal to pine. These results indicate that a cement/ wood ratio of approximately 5/1 was the lowest at which southern hardwood- cement mixtures can be cured naturally without heating or pressing. In general, mixtures made of cold-stored wood were stronger than those made of air-dried wood at higher cement/wood ratios. But, at lower cement/wood ratios, mixtures with air-dried wood had higher compressive strength than those with cold-stored wood. This confirms that at lower cement/wood ratios used in com- mercial production, air-dried wood is more compatible with cement than cold- stored wood. As shown in Fig. 2, the time required to reach maximum temperature was inversely proportional to the maximum temperature reached. A faster reaction time and higher hydration temperature occurred at higher cement/wood ratios. Southern pine and hardwood followed two different hydration time-temperature curves. Southern pine-cement mixtures required much shorter time than hard- wood-cement mixtures to reach the same maximum hydration temperature. A further analysis (Table 4) indicates that changing cement/wood ratios had a much greater impact on hardwoods than southern pine. This impact is more significant when cement/wood ratios approach the lower end. This implies that research results from mixtures with high cement/wood ratio may not apply directly to those commercial processes using lower cement/wood ratio. REFERENCES AMERICAN SOCIETY OF TESTING AND MATERIALS. 1983. Annual Book of ASTM Standards, vol. 04.02. C39-83b. BIBLIS, E. J., AND C. F. LO. 1968. Sugars and other wood extractives effect on the setting of southern pine-cement mixtures. Forest Prod. J. 18(8):28-34. ELMENDORF RESEARCH LABORATORIES, INC. OF PALO ALTO, CALIFORNIA. 1954. U.S. Patent No. 2,697,677. LEE, A. W. C. 1984. Physical and mechanical properties of cement bonded southern pine excelsior board. Forest Prod. J. 34(4):30-34. . 1985. Bending and thermal insulation properties of cement-bonded cypress excelsior board. Forest Prod. J. 35(11/12):57-58. 268 WOOD A N D  FIBER SCIENCE, JULY 1987, V. 19(3) -, AND Z. HONG. 1986. Compressive strength of cylindrical sample as an indicator of wood- cement compatibility. Forest Prod. J. 36(11/12):87-90. LIU, Z., AND A. A. MOSLEMI. 1985. Influence of chemical additives on the hydration characteristics of western larch wood-cement-water mixtures. Forest Prod. J. 35(7/8):37-43. MOSLEMI, A. A,, J. F. GARCIA, AND A. D. HOFSTRAND. 1983. Effect of various treatments and additives on wood-Portland cement-water systems. Wood Fiber Sci. 15(2): 164-1 76. -, AND Y. T. LIM. 1984. Compatibility of southern hardwoods with Portland cement. Forest Prod. J. 34(7/8):22-26. WEATHERWAX, R. C., AND H. TARKOW. 1964. Effect of wood on setting of Portland cement. Forest Prod. J. 14(12):567-570. -, AND - . 1967. Effect of wood on the setting of Portland cement: Decayed wood as an inhibitor. Forest Prod. J .  17(7):30-32. 

Effect of Cement/Wood Ratios and Wood Storage Conditions on Hydration Temperature, Hydration Time, and Compressive Strength of Wood-Cement Mixtures

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Effect of Cement/Wood Ratios and Wood Storage Conditions on Hydration Temperature, Hydration Time, and Compressive Strength of Wood-Cement Mixtures

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