Suitability of fibers from mountain pine beetle attacked wood in wood-cement composite materials.
This study used hydration tests to investigate the suitability of fibers from mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins.) infected wood for the production of wood-cement composites. Four different types of lodgepole pine (Pinus contorta var. latifolia Engelm.) fibers (fibers from two different log sizes and two different years since tree death (3 and 5 years)) and two types of yellow cedar fibers of different fiber sizes were considered in this study. Two cement types, various fiber/cement/water ratios, and a range of additive conditions were also studied to identify potential formulations for prototype development. The results showed that the 3-years-since-tree-death fibers from small logs (diameter < 11 inches) with type III cement and calcium chloride (Ca[Cl.sub.2]) as the additive would be the best formulation. The other fiber types with additives also showed good results. Since increasing the additive/fiber ratio tended to result in a greater hydration rate. Finally, the type of cement also affected the results. Due to its finer particle structure, the Portland cement type III had improved performance. Since differences are expected between laboratory testing and large-scale industry trials, further studies are needed to verify these results.
The current mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins.) infestation in British Columbia, Canada, is the most destructive biotic agent of mature pine forests in western North America. Outbreaks have been observed in all pine species; however, they have occurred principally in lodgepole pine (Pinus contorta vat. latifolia Engelm.) (Taylor et al. 2006), which is one of the most important commercial softwood species in North America. Aerial overview surveys from 2005 showed that the MPB infestation had reached about 8.7 million hectares of British Columbia forests in the red-attack stage. This was an increase from a little more than seven million hectares the previous year. The red-attack stage occurs in the year following the initial attack (green-attack stage). The needles turn red after the beetles have left the tree, indicating that the tree is dead: the fungi carried by the beetles have cut the tree off from its supply of water and nutrients. In subsequent years, the needles fall off the trees (grey-attack stage). This vast volume of available MPB wood fiber needs to be utilized in a timely manner before further deterioration of the standing dead timber occurs. It is also known that processing of the dry MPB logs can lead to the generation of more fine material and residues compared to healthy, green logs. There is a need to investigate alternative value-added wood-based products that can make use of the fine material and residues from the processing of the MPB logs.
Cement-bonded board (CBB) combines the properties of two important materials: cement and any fibrous materials, like wood or agricultural residues. It is a panel product made up of strands, flakes, chips, particles or fibers of wood, or some agricultural residues, bonded with ordinary Portland cement (Eusebio 2003).
The wood fiber is used to replace asbestos in the manufacture of fiber cement products because of its reduced health hazard, high availability, low density, low cost, low energy demand during manufacture, and good reinforcement properties, despite having lower mechanical properties compared to some synthetic fibers (Campbell and Coutts 1980). Cement-bonded board has gained favor throughout the building industry (Eusebio 2003). Extensive studies on the expansion of the raw material base have demonstrated the feasibility of producing CBB using tropical hardwood species, some agricultural wastes (agri-wastes) and even industrial residues (Fernandez and Taja-on 2000, Warden et al. 2000, Eusebio 2003).
Prior to producing cement-bonded particleboard, debarked logs are stored for at least 2 to 3 months to reduce their moisture and sugar content (Evans 2000). In addition, degradation of wood fiber's hemicellulose improves wood-cement bonding strength (Canadian Wood Council 1997). The chemical components of MPB fibers with lowered sugar and hemicellulose content may be regarded as a potential advantage in producing wood-cement composite products (Woo et al. 2005).
Other production parameters can also affect CBB properties: the material (wood/cement, agri-wastes/cement) ratio; the water/cement ratio; the type of wood or agri-waste; and, the cement setting accelerators. Eusebio (2003) and Govin et al. (2006) reported that the addition of wood strongly delayed the hydration process. Lee et al. (1987) indicated that hydration temperature was drastically reduced, hydration time was prolonged, and compressive strength was reduced as the cement/wood ratio decreased. Some studies also indicated that additives may enhance the compatibility of wood/cement/ water mixtures and accelerate cement hydration (Moslemi et al. 1983, Semple and Evans 2000).
Ma et al. (2000) studied the relationship between the hydration energy released on the manufacture and mechanical properties of cement-bonded boards, and indicated that the total energy release is a quick way to determine a suitable mixture of cement additives and fibers. A positive correlation between the maximum temperature of hydration and the time to reach the maximum temperature, and the modulus of rupture (MOR) and internal bonding of wood-cement composites was also found by Wei et al. (2000). Therefore, the hydration test may be used as a predictor of the general inhibitory properties and feasibility of the raw material prior to the manufacture of cement-bonded boards.
The objective of this study was the investigation of the compatibility of MPB fibers for producing wood-cement products via hydration tests in different conditions and to identify optimal formulations for further prototype developments.
Materials and methods
In this study, five kinds of fibers were studied. They include 4 types of lodgepole pine fibers obtained from logs from the Vanderhoof area of British Columbia, and yellow cedar (Chamaecyparis nootkatensis) fiber (Y-R) from the west coast of British Columbia. The lodgepole pine logs were small logs (diameter at butt less than 11 inches) from 3-years-since-death trees (3S), large logs (diameter at butt greater than 11 inches) from 3-years-since-death trees (3L), small logs from a 5-years-since-death trees (5S), and large logs from 5-years-since-death trees (5L). Yellow cedar fiber, known to be suitable in CBB production, served as a benchmark for the study. The fibers were processed in a Willey mill with materials passing through a 2 mm screen.
Portland cement type I (Lehigh brand, general use Portland cement) and type III (Lehigh brand, high early strength, hydraulic cement) were used to compare the effects from the different cement types. Type I cement is typically used in the wood-cement industry. Type III is chemically similar to type I but is ground finer. This can provide more reaction surfaces for hydration to occur. In addition, two common additives, magnesium chloride (Mg[Cl.sub.2]) and calcium chloride (Ca[Cl.sub.2]), were used to study the effects of different additives and contents.
The whole experimental plan was separated into two parts: part 1 involved using the fiber/cement/water ratio as 15/200/ 90.5 based on dry weight and 3 percent additive, based on cement weight, to test different conditions on the interaction of different variables, including the types of cement, fiber, and additive. Water came from 3 different sources: water in the fiber, water in the Ca[Cl.sub.2] solution, and water that was added (Lee et al. 1987). There were 3 replicates for each condition. In addition, the control samples (neat cement) were tested using a cement/water ratio of 200/80 based on ovendry weight.
Part 2 involved evaluating different fiber/cement/water ratios and different additive contents with the condition selected according to the results of part 1. The cement and fiber were mixed with the following fiber/ cement ratios: 1/10, 1/8, 1/5 and 1/4. The amount of water was 2.7 mL per gram of fiber and 0.25 mL per gram of cement (Weatherwax and Tarkow 1964, 1967). Finally, different additive contents--5, 8, 10, and 15 percent, based on cement weight--were tested in order to find the effects of additive content on wood-cement compatibility.
Fifteen grams of wood fiber and 200 g of fresh dry cement were added in a sealable grip polyethylene bag and mixed thoroughly. Six grams of additive (3% of the cement weight) were added into 90.5 g distilled water and then mixed with the mixture of cement and fiber. The process involved kneading by hand for around 3 minutes. Immediately after the mixing of the hydration sample, a temperature thermocouple (type T) was inserted into the mixture in the sample bag and enclosed within the body by folding the bag and contents around it. The specimen was then placed in the wood testing boxes with 50 mm (2 inch) thick Styrofoam boards for insulation. The hydration process was carried out for 28 hours. Temperatures were recorded at 15 minute intervals using a data logger. The temperature vs. time curves were smoothed by plotting the progressive average of each successive reading. The equation of the hydration rate is (R) = ([T.sub.max] - [T.sub.min])/[t.sub.max] ([degrees]C/h), where Tmax is the maximum temperature of hydration, [t.sub.max] is the time to reach Tmax, and Train is the minimum temperature attained during the first 5 hours of hydration. The hydration reaction of the cement with some wood species indicated that, within a 24-hour observation period, there was an exothermic peak with a maximum temperature that represented cement setting. The time to attain the maximum temperature of hydration was considered the required setting time of the mixture (Wei et al. 2000). In this study, all experiments were done in a constant climate room, the condition of which was maintained at 20 [+ or -] 1 [degrees]C and 65 [+ or -] 5 percent R.H.
Results and discussion
The results of the first series of tests with the 4 different types of lodgepole pine fibers in various conditions are presented in Table 1. The data were analyzed using Duncan's multiple range test for analysis of variance (ANOVA). According to the Duncan groupings (Table 2), the formulation, 3S fiber with Portland cement type III and Mg[Cl.sub.2], resulted in the highest maximum temperature. The 3S fiber with Portland cement type III and Ca[Cl.sub.2], resulted in the shortest [t.sub.max] and the highest hydration rate. We chose this formulation, 3S-type III-Ca[Cl.sub.2] to carry out the following tests about the effects of different fiber/cement/water ratios and various contents of additive on the hydration rate.
Comparison of the effects of two cement types on the same fiber
As Figure 1 shows, cement type affects the hydration results. Type III Portland cement apparently produced a higher hydration rate than type I for the different fibers and additive types. As type III cement has the characteristics of finer particles, shorter reaction time, and improved early strength, these results can be expected. However, type III cement costs more than type I cement. Using type I cement with effective additives may be a good option. When additives were used, for both type I and type III cement, the hydration rate became higher in every type of fiber considered, even higher than in neat cement. Moreover, Ca[Cl.sub.2] results had higher hydration rates for all types of fibers compared to those of Mg[Cl.sub.2]. The effect of additives on hydration will be discussed later.
Besides hydration rate, two other indices, [T.sub.max] and [t.sub.max], were obtained on the control group of the various fibers. [T.sub.max] and [t.sub.max] in cement type I were approximately 40 [degrees]C and 14 to 16 hours, respectively, and in cement type III approximate 60 [degrees]C and 11 to 13 hours, respectively. Compared to neat cement, which is around 70 [degrees]C and 10 hours in neat cement type I and around 85 [degrees]C and 9 hours in neat cement type III, the hydration of samples incorporating wood fibers yielded less than suitable results. The wood-cement mixtures had a longer reaction time and a lower maximum temperature. According to the research of Sandermann and Kohler (1964), a [T.sub.max] of hydration less than 50 [degrees]C means the mixture is unsuitable. In addition, a [T.sub.max] of 50 to 60 [degrees]C is intermediately suitable; and, a [T.sub.max] greater than 60 [degrees]C is suitable (Karade et al. 2003).
With additives, however, the results were greatly improved. When using Ca[Cl.sub.2], the [T.sub.max] reached 68 to 73 [degrees]C in cement type I and 77 to 82 [degrees]C in cement type III; and, when using Mg[Cl.sub.2], the [T.sub.max] rose to 68 to 76 [degrees]C in cement type I and 78 to 83 [degrees]C in cement type III. Furthermore, when using Ca[Cl.sub.2], [t.sub.max] was reduced to around 3 to 4 hours in cement type I and around 3 to 3.5 hours in cement type III. When using Mg[Cl.sub.2], [t.sub.max] decreased to around 5 to 7 hours in cement type I and around 5 to 6.5 hours in cement type III. The results are comparable to those of neat cements. In addition, the results indicate that, although the formulations with Ca[Cl.sub.2] showed a lower [T.sub.max], the [t.sub.max] could be 2 to 3 hours faster than formulations with Mg[Cl.sub.2] in cement types I and III. Consequently, the formulation with Ca[Cl.sub.2] resulted in higher hydration rates for cement types I and III.
Effect of fiber size on the hydration result
In order to examine the effect of fiber size on the hydration results, we also conducted the test with yellow cedar fiber in different sizes, passing through a 1.18 mm (14-mesh) screen (Y-r) to give particles of around 2 to 3 cm in length, and passing through a 2 mm (10-mesh) screen (Y-g) to give particles around 2 to 4 mm in length. In other words, one type of fiber was long and thin, and the other had a particle type shape. The results and analysis of variance (5% level) are presented in Table 3.
The results of Y-r and Y-g were very similar in all indices. The results of ANOVA also showed that there were no significant differences between Y-r and Y-g. It implied that the range of fiber size considered may not significantly affect the hydration results of wood-cement mixtures. However, Badejo (1988) has reported that the use of longer and thinner flakes results in stronger, stiffer, more dimensionally stable cement-bonded boards. Furthermore, other studies on the effects of fiber size have reported that relatively fine panicles are suitable for comparing the compatibility of different wood species in the laboratory. However, these results may not be valid under commercial manufacturing conditions using a range of different particle sizes (Weatherwax and Tarkow 1964, Semple et al. 1999, Karade et al. 2003). Therefore, the fiber size factor may be a consideration during product manufacturing, even though it may not affect hydration test results.
Effect of fiber types on the hydration rate
We compared the hydration rate of various fiber types with different additive conditions in the two cement types separately, in order to consider the effect of the fiber type. The results are presented in Figure 2. ANOVA ([alpha] = 5%) showed that there was no difference between the fiber types in cement types I and III (Table 4 A-B).
When the results of the 3 additive conditions were separated and the data of the hydration rate amongst the various fiber types in the two cement types were analyzed using ANOVA (Table 5), the results showed no significant differences among fiber types in the control and Ca[Cl.sub.2] groups. In contrast, Mg[Cl.sub.2] resulted in a significant difference among fiber types. This may be attributed to possible interactions between the various fibers and Mg[Cl.sub.2].
Effects of various fiber/cement/ water ratios on the hydration rate
In past research on wood-cement compatibility, experiments were typically carried out in the laboratory using a mixture with the fiber/cement ratio of 15/200 (1/13.3). However, this ratio is much different from that used in commercial cement-bonded products, which usually use about 20 percent fiber, 60 percent cement and 20 percent water by weight (about 1/3/1) (Evans 2000); and the low fiber/cement ratio would overshadow the effects of the species of treatments on the hydration characteristics, especially when an effective additive is added to the mixture (Lee and Hong 1986). Hence, this study investigated the effects of various ratios on hydration.
According to the earlier results in this study, the formulation that resulted in the highest hydration (3S fibers with type III Portland cement and 3 percent Ca[Cl.sub.2]) was chosen to research various fiber/cement/water ratios. The cement and fiber were mixed with the following fiber/cement ratios: 3/40, 1/10, 1/8, 1/5, 1/4. The amount of water was 2.7 mL per gram of fiber and 0.25 mL per gram of cement. Therefore, the fiber/ cement/water formulations (in g/g/g) for testing were 15/200/ 90.5, 20/200/104, 25/200/117.5, 40/200/158, and 50/200/185. The results are shown in Table 6.
All of the previous studies indicated that the fiber/cement/ water ratio had a significant effect on wood-cement compatibility. The results of our test generally confirmed those of previous studies. As shown in Figure 3, the faster reaction time and higher maximum temperature occurred at lower fiber/cement ratios. However, Lee et al. (1987) tried different ratios and suggested that research results from mixtures with low fiber/cement ratios may not apply directly to commercial processes; moreover, some research indicated that the hydration results may not predict the suitability for all kinds of fibers in the manufacture of CBB products (Semple et al. 1999). Consequently, further study is needed to develop conclusions that can be generalized.
Effects of additive content on the hydration rate
In order to find the effect of additive content on wood-cement compatibility, the additive Ca[Cl.sub.2] was incorporated, in amounts of 5 percent, 8 percent, 10 percent, and 15 percent, based on cement weight, with the mixture of 3S fibers and type III Portland cement at a 15/200/90.5 (g/g/g) fiber/ cement/water ratio. The results showed that additives have a highly beneficial effect on the hydration rate, as shown in Table 6. The hydration rate increased with the addition of additive content. For example, as the content of the Ca[Cl.sub.2] additive increased from 0 percent to 15 percent (Fig. 4), the mean [T.sub.max] increased from 62.3 [degrees]C (0%) to 105.4 [degrees]C (15%), and mean [t.sub.max] decreased from 11 hour (0%) to 0.75 hour (15%). Test results imply that additives can significantly improve hydration results.
In a study by Ma et al. (2000), where various levels of different types of additives were evaluated, the results also showed the same tendency for all types of additives. Therefore, the addition of higher levels of additives in general appears to produce faster and improved hydration.
To increase the use of MPB-attacked wood, incorporation of its fiber into composite materials is a good option. However, the suitability of this kind of fiber for composite materials should be studied carefully. The chemical components of the MPB fibers, with the reduced sugar and hemicellulose content, may offer potential advantages in producing wood-cement composite products.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
In this study, we could see that the MPB fibers' performance on hydration resulted in higher [T.sub.max] shorter time to reach [t.sub.max], and greater hydration rate after the incorporation of additives. In addition, Portland cement type III resulted in good hydration rates because of its finer structure. Using type III cement with Ca[Cl.sub.2] or Mg[Cl.sub.2] could produce great improvements in the compatibility of MPB fibers used in wood-cement products: Ca[Cl.sub.2] performed better in achieving a shorter [t.sub.max] than Mg[Cl.sub.2]. Although the addition of additive content has beneficial results, the addition of the fiber may not have resulted in better results. Consequently, considering these factors, the prototype development of CBB with MPB should be evaluated carefully to obtain an optimal formulation with additional consideration of the physical, durability, and strength properties of the wood-cement products.
The results of laboratory hydration test may not be directly applied in real product processing, since different fiber/ cement ratios are used in lab testing samples and in products in the marketplace. Therefore, it is recommended that further studies for prototype products are needed to verify these results.
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Frank Lam *
The authors are, respectively, PhD Student and Professor, Dept. of Wood Sci., Univ. of British Columbia, Vancouver, British Columbia, Canada (email@example.com, franklam@ interchange.ubc.ca). This work was financially supported by Forestry Innovation Investment Ltd. under British Columbia's mountain pine beetle initiative Project No. MDP-07-020C, "Development of MPB wood plastic and wood cement products." This paper was received for publication in May 2007. Article No. 10350.
* Forest Products Society Member.
Table 1.--Average hydration rate of different conditions, with corresponding maximum temperature and time. [T.sub.max]([degrees]C) Fiber Group Cement type I Cement type III 3S Control 40.2 62.3 Ca[Cl.sub.2] 71.6 82.5 Mg[Cl.sub.2] 71.7 82.6 3L Control 39.6 58.1 Ca[Cl.sub.2] 70.4 78.7 Mg[Cl.sub.2] 73.4 80.9 5S Control 43.7 59.2 Ca[Cl.sub.2] 69.8 78.5 Mg[Cl.sub.2] 72.0 80.9 5L Control 39.8 57.7 Ca[Cl.sub.2] 68.8 78.2 Mg[Cl.sub.2] 76.6 80.8 neat cement 69.6 84.8 [t.sub.max](h) Fiber Group Cement type I Cement type III 3S Control 15.7 11.0 Ca[Cl.sub.2] 3.4 3.1 Mg[Cl.sub.2] 6.1 5.5 3L Control 16.3 12.7 Ca[Cl.sub.2] 3.8 3.3 Mg[Cl.sub.2] 5.8 5.9 5S Control 14.1 11.8 Ca[Cl.sub.2] 3.7 3.1 Mg[Cl.sub.2] 5.5 4.8 5L Control 14.8 12.4 Ca[Cl.sub.2] 3.8 3.3 Mg[Cl.sub.2] 5.2 5.0 neat cement 9.8 8.9 Hydration rate([degrees]C/h) Fiber Group Cement type I Cement type III 3S Control 0.8 3.1 Ca[Cl.sub.2] 11.2 13.7 Mg[Cl.sub.2] 6.8 9.3 3L Control 0.8 2.5 Ca[Cl.sub.2] 10.2 11.8 Mg[Cl.sub.2] 7.2 8.6 5S Control 1.2 2.7 Ca[Cl.sub.2] 10.1 12.4 Mg[Cl.sub.2] 7.4 10.1 5L Control 0.9 2.5 Ca[Cl.sub.2] 9.6 11.4 Mg[Cl.sub.2] 8.5 9.9 neat cement 4.4 6.5 Table 2.--Comparison of various formulations by the hydration rate. Hydration rate Duncan grouping * Formulation ([degrees]C/h) 3S-type III-Ca[C1.sub.2] 13.71 A 5S-type III-Ca[Cl.sub.2] 12.43 B 3L-type III-Ca[Cl.sub.2] 11.82 C 5L-type III-Ca[Cl.sub.2] 11.40 C D 3S-type I-Ca[Cl.sub.2] 11.18 D 3L-type I-Ca[Cl.sub.2] 10.22 E 5S-type III-Mg[Cl.sub.2] 10.15 E 5S-type I-Ca[C1.sub.2] 10.15 E 5L-type 111-Mg[Cl.sub.2] 9.93 E 5L-type I-Ca[Cl.sub.2] 9.65 EF 3S-type III-Mg[Cl.sub.2] 9.27 F 3L-type 111-Mg[C1.sub.2] 8.59 G 5L-type I-Mg[Cl.sub.2] 8.54 G 5S-type I-Mg[C1.sub.2] 7.41 H 3L-type I-Mg[Cl.sub.2] 7.24 HI 3S-type I-Mg[Cl.sub.2] 6.76 l 3S-type III-control 3.11 J 5S-type III-control 2.71 JK 3L-type III-control 2.47 K 5L-type 111-control 2.47 K 5S-type I-control 1.16 L 5L-type I-control 0.90 L 3S-type I-control 0.82 L 3L-type I-control 0.82 L * The same letters mean that there is no significant difference in between. Table 3.--Results of analysis of variance for different fibersizes of yellow cedar by the hydration rate. Hydration rate ([degrees]C/h) Cement Fiber Control Ca[Cl.sub.2] Cement type I Y-r 1.4 9.7 Y-g 1.7 10.0 Cement type III Y-r 2.6 9.8 Y-g 2.6 11.5 Hydration rate ([degrees]C/h) Cement Fiber Mg[Cl.sub.2] F Tabular F Cement type I Y-r 5.7 1.60 (ns) 18.51 Y-g 5.6 Cement type III Y-r 8.1 2.91 (ns) Y-g 7.4 (ns): not significant Table 4.--Analysis of variance of the results of the hydration rate by various fiber types in (A) cement type l, and (B) ce- ment type III. A Sum of Mean Source of variation squares df square Fiber type 3.303248 4 0.825812 Additive condition 23.85173 1 23.85173 Error 3.372286 4 0.843071 Total 30.52726 9 A Tabular Source of variation F P-value F-value Fiber type 0.98 0.508 6.389 Additive condition 28.29 0.006 7.71 Error Total B Sum of Mean Source of variation squares df square Fiber type 6.692281 4 1.67307 Additive condition 15.70082 1 15.70082 Error 2.110466 4 0.527616 Total 24.50357 9 B Tabular Source of variation F P-value F-value Fiber type 3.17 0.145 6.39 Additive condition 29.76 0.005 7.71 Error Total Table 5.--p-value (a) of analysis of variance for the results of the hydration rate by various fiber types in different additive conditions. Additive condition Factor Control group Ca[Cl.sub.2] Mg[C1.sub.2] Fiber type 0.612 0.0564 0.007 Cement type 0.0004 0.0053 0.0003 (a) p-value<0.05 = no significant difference. Table 6.--Hydration rate ([degrees]C/h) of the formulation 3S-type III cement-Ca[Cl.sub.2] in different conditions. Wood/cement/ Ca[Cl.sub.2] content (a) water ratio (h) 0% 3% 5% 8% 10% 15% 50/200/185 3.5 40/200/158 5.6 25/200/117.5 10.2 20/200/104 9.2 15/200/90.5 3.1 13.7 18.5 27.9 33.5 66.2 Neat cement 6.5 (a) Ca[Cl.sub.2] content based on cement weight (g). (b) The ratio based on dry weight (g/g/g). Figure 1.--Comparison of two cement types by the hydration rate of lodgepole pine fire A.3S, B.3L, C.5S, and D.5L, in different additive conditions, with 95 percent confidence interval. A. 3S Cement Cement Additive Type type I type III control 0.8 3.1 Ca[Cl.sub.12] 11.2 13.7 Mg[Cl.sub.12] 6.8 9.3 neat cement 4.4 6.5 B. 3L Cement Cement Additive Type type I type III control 0.8 2.5 Ca[Cl.sub.12] 10.2 11.8 Mg[Cl.sub.12] 7.2 8.6 neat cement 4.4 6.5 C. 5S Cement Cement Additive Type type I type III control 1.2 2.7 Ca[Cl.sub.12] 10.1 12.4 Mg[Cl.sub.12] 7.4 10.1 neat cement 4.4 6.5 D. 5L Cement Cement Additive Type type I type III control 0.9 2.5 Ca[Cl.sub.12] 9.6 11.4 Mg[Cl.sub.12] 8.5 9.9 neat cement 4.4 6.5 Note: Table made from bar graph. Figure 2.--Hydration rate of various fiber types with different additive conditions in A. type I cement and B. type III, with 95 percent confidence interval. A. cement type I Fibre Type control Ca[Cl Mg[Cl .sub.12] .sub.12] 3S 0.8 11.2 6.8 3L 0.8 10.2 7.2 5S 1.2 10.3 7.4 5L 0.9 9.6 8.5 Y-r 1.4 9.7 5.7 Y-g 1.7 10.0 5.6 B. cement type III control Ca[Cl Mg[Cl Fibre Type .sub.12] .sub.12] 3S 3.1 13.7 9.3 3L 2.5 11.8 8.6 5S 2.7 12.4 10.1 5L 2.5 11.4 9.9 Y-r 2.6 9.8 8.1 Y-g 2.6 11.5 7.4 Note: Table made from bar graph.
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|Author:||Chang, Feng-Cheng; Lam, Frank|
|Publication:||Forest Products Journal|
|Date:||Mar 1, 2008|
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