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Geopolymer concrete (GPC) is a cutting-edge, environmentally friendly substance which replace cement, resulting in a significant decrease in carbon emissions and encouraging the adoption of more sustainable construction methods. The objective of this study is to evaluate the likelihood of Alkali-Silica Reaction (ASR) occurring in geopolymer concrete by using local aggregates, sourced from various places. The examination was conducted while employing the ASTM C 1260 test method, which entailed measuring the expansion of test bars over a period of 150 days. Additionally, compressive strength testing is performed by casting cubes, and flexural strength tests were performed by casting prisms. In addition, samples of ordinary Portland cement (OPC) were subjected to testing for comparison. The findings demonstrated that the expansion of GPC bars adhered to the limitations set by ASTM C 1260, with an expansion rate of less than 0.025% after 28 days. On the other hand, the OPC samples showed ASR growth that was greater than 0.2% after 28 days, which went over the limitations set by the ASTM standard. Furthermore, the GPC samples exhibited a notable enhancement in both compressive and flexural strength, with compressive strength showing a 15–25% improvement and flexural strength increasing by 5–15% even in harsh environmental conditions. However, OPC samples exhibited a decrease of up to 6% in compressive strength and 5% in flexural strength under same conditions. The findings indicate that geopolymer concrete provides greater resistance to ASR, improved durability, and an extended lifespan in comparison to OPC. [ABSTRACT FROM AUTHOR]

The physico-mechanical quality of the seed bed is extremely important not only for the soil air-water dynamics, but also for the germination, seedling emergence, and development of the plants. The crust layer formed after precipitation and irrigation in soils with poor structural properties is among the most important indicators of the lower seedbed quality. While there are different applications to increase the physico-mechanical quality of the seedbed, there are also cement applications that provide rapid aggregate formation and stability. The effects of cement application on the soil mechanical quality and seedling emergence of clay textured soil with poor structural characteristics were investigated in the present study. For this purpose, a total of 36 small plots with a size of 2.4 m2 were created. Cement was applied at 0.25–0.5–1 and 2% doses to 18 plots in the fall period, and to the other 18 plots in the spring period. After the treatment, soil samples were taken for analysis before the planting period and the number of seedling emergence was determined by planting the bean plant during the planting period. According to the results of the study, it was found that cement applied in two periods caused an increase in soil aggregate stability, decreased penetration resistance, modulus of rupture, and dispersion rate, and increased water holding capacity to a limited extent. On the other hand, cement application also had positive impacts on the emergence of the bean plant. The 1% dose of the spring application of cement was more effective on the determined soil structural characteristics and seedling emergence. [ABSTRACT FROM AUTHOR]

The air voids in the bituminous mix are filled with a cementitious grout to create cement grouted bituminous (CGB) mix, which is a semi-flexible material. The material has a high resistance to permanent deformation at high temperatures and under heavy loads because of the cementitious grout used in the mixture. Despite their increased brittleness, CGB layers are more prone to cracking when used as thin (40–60 mm) surface or base layers. Increase in binder content in mix decreases air void content and grout content, which leads to reduction in rutting resistance and expected to improve the fatigue cracking resistance. The results of an investigation into the impact of aggregate gradation and binder content on the fatigue performance of CGB mixes are presented in this paper. In a four-point bending test mode at 25 °C, beam specimens of CGB Mixes made with four different aggregate gradations and four different binder contents were tested at four strain levels. The fatigue life measured at higher strain levels of 225 and 250 µε and various mechanical properties like indirect tensile strength and modulus of rupture showed good correlation. By analysing pavements with CGB layers used as the base or surface layer, the fatigue cracking susceptibility of the CGB layer in a typical highway pavement has been determined. It has been found that using the CGB mix as the surface layer is a good choice because the mix also provides a very strong rut as well as an oil and chemical-resistant layer. [ABSTRACT FROM AUTHOR]

The effects of cattail/poplar straw weight ratio, sandwich panel thickness, and the number of kraft paper layers at the core of sandwich panels on the modulus of rupture (MOR) of the panels were predicted using an artificial neural network (ANN) and an adaptive neuro-fuzzy inference system (ANFIS). The prediction accuracy of the MOR based on experimental data, in terms of the mean absolute percentage error, was smaller than 1.4 and 1.1%, with coefficients of determination 0.94 and 0.995 for the ANN and ANFIS models, respectively. These models can easily predict the bending strength of lignocellulosic-based sandwich panels with a high precision in the manufacturing process. [ABSTRACT FROM AUTHOR]

The present experimental and numerical study investigates the impact of coarse recycled concrete aggregate (CRCA) on the short and long-term properties of self-compacting concrete (SCC) subjected to different curing temperatures. In addition, finite element analysis (FEA) was utilized to estimate the total shrinkage of the SCC. Three CRCA replacement ratios (0%, 50%, and 100%) and three temperatures (20 °C, 35 °C and 50 °C) were chosen as the two main parameters. The results reveal that the mechanical performance of SCC mixes generally weakened with increased CRCA replacement ratio. The reductions were 11%, 13% and 7% as compared to the control mix, for the compressive strength (fc), modulus of rupture (Mr) and elastic modulus (Ec), respectively, when a 50% CRCA replacement ratio was used. Furthermore, the total shrinkage of SCC mixes increases considerably both with increases in curing temperature and in CRCA percentage. For the same room temperature (20 °C), the total shrinkage increased by 20% and 60%, corresponding to the addition of 50% and 100% of CRCA, while for the SCC mixtures subjected to a temperature of 50 °C, the increases were 23% and 14%, respectively. Finally, the total shrinkage results obtained by the FEA are very close to the measured values. It is recommended to use 50% and 100% CRCA for manufacturing new SSC mixture, which seems to be a high-appropriate solution. [ABSTRACT FROM AUTHOR]

It is well-know that PC is vulnerable to sudden failure under 'tensile' and/or 'flexural' loading; hence, it yields large structural dimensions when used for tensile load applications. A discrete fiber-reinforcement advances the ductility and tensile strength of Plain concrete (PC); therefore, Fiber-reinforced concretes (FRCs) require structural dimensions smaller than PC under same tensile loading conditions. In this study, the effect of fiber type and content is evaluated and analyzed on the life cycle cost and CO2-footprint of concrete pavement. Namely three types of fiber-reinforced concretes, i.e., Steel fiber-reinforced concrete (SFC), Glass fiber-reinforced concrete (GFC), and Polypropylene fiber-reinforced concrete (PFC) were considered for pavement application and three different fiber contents, i.e., 0, 0.5 and 1% (by volume). For the case study, location of design pavement was considered in the Islamabad city. Pavement thickness was designed for three types of streets, i.e., residential, collector, and major arterial (consideration for low to high traffic volumes). Analysis of results revealed that for different loading conditions or types of streets, PC pavement produces higher CO2-emission and is uneconomical compared to the FRC pavements. The results show the superiority of SFC over GFC and PFC in overall mechanical performance. SFC has higher associated footprint than other FRCs. Despite lesser mechanical performance compared to SFC; GFCs and PFCs show the highest reductions in the cost and CO2-footprint of the pavement (i.e., Cost per unit area of pavement (CPA) and Global warming potential per unit area of pavement (GWPPA)). [ABSTRACT FROM AUTHOR]

This study used near-infrared (NIR) spectroscopy to predict mechanical properties of wood. NIR spectra were collected in wavelengths 900–1700 nm, and spectra averaged by radial and tangential surface spectra were used to establish a partial least square (PLS) model based on correlation local embedding (CLE). Mongolian oak (Quercus mongolica Fisch. ex Ledeb.) was used to test the effectiveness of the model. The cross-validation method was used to verify the robustness of the CLE–PLS model. Ninety samples were tested as the calibration set and forty-five as the validation set. The results show that the prediction coefficient of determination ( R p 2 ) is 0.80 for MOR, and 0.78 for MOE. The ratio of performance to deviation is 2.23 for MOR and 2.15 for MOE. [ABSTRACT FROM AUTHOR]

Rapid growth rates and the accompanying reduced rotation ages of forest plantations have resulted in increased proportions of juvenile wood. Growing space markedly influences growth rate and may be manipulated by stand density management. The objective of this study was to evaluate the effect of stand density on the modulus of elasticity (MOE), modulus of rupture (MOR) and other selected properties of young (16–20 years) South African-grown Pinus patula lumber. Thirty-seven trees from two commercial stands were processed into 71 logs, cant sawn into lumber and tested for MOE, MOR, wood density and distortion. The first stand was planted at 1334 stems ha−1 and thinned to 827 stems ha−1 at age 11. The second stand was planted at 1667 stems ha−1 and was unthinned. Lumber from a previous study on 17 different commercial stands from more conventional (lower) stand density management regimes was also analysed using linear mixed-effect models. Only lumber from the 1667 stems ha−1 stand conformed to the requirements for structural use and had a considerably higher mean MOE of 8967 MPa compared to 7134 MPa for the 1334/827 stems ha−1 stand and 5556 MPa for the more conventional stands. MOR values were adequate for all stands. Unlike previous studies on other species, slenderness did not seem to have a profound effect on the MOE of the lumber from these P. patula trees. Stand density management therefore has the potential to increase lumber stiffness of P. patula and should be considered as a forest management intervention for wood quality improvement by saw-log growers in South Africa. [ABSTRACT FROM AUTHOR]

The modulus of elasticity (MOE) and modulus of rupture (MOR) were evaluated for 190 pieces of dimension lumber (2 by 4 lumber, 38 by 89 mm in cross-section) produced from Larix sibirica trees grown in Mongolia. The 5% tolerance limits of the MOE and MOR were 5.70 GPa and 15.1 MPa, respectively. The value of the 5% tolerance limit of the MOR exceeded the characteristic value of 2 by 4 lumber in visual grading class No. 3 of the Japanese Agricultural Standard for the D. fir-L, Hem-Tam, JS-III and S-P-F softwood species groups. A significant positive correlation was found between the MOE and MOR, although air-dry density was weakly correlated with bending properties in L. sibirica. [ABSTRACT FROM AUTHOR]

Ceramic shell mould plays a key role in achieving dimensional accuracy and quality of casting. This work investigates the effect of mould parameters such as silica concentration, filler to binder ratio and the number of secondary coats on mould properties, namely modulus of rupture, adjusted fracture load, and permeability. Experimental results report that enrichment in silica results in drastic growth in adjusted fracture load with a small increase in modulus of rupture and no change in permeability. Improvement in filler to binder ratio causes a significant increase in the adjusted fracture load and modulus of rupture with moderate decrease in permeability. An increase in number of ceramic coats increases the adjusted fracture load significantly and reduces permeability moderately. Impact of the adjusted fracture load on casting shrinkage has been studied by conducting various casting trials. Adjusted fracture load above 315 N is preferred which corresponds to 25–30% silica, filler to binder ratio of 1.25 and number of secondary coats as six to eight for reduced shrinkage variation. [ABSTRACT FROM AUTHOR]

Fused silica is widely used in investment casting shell molds as flour, stucco and binder for its superior properties, such as low linear thermal expansion coefficient and high thermal shock resistance. Investment shell molds are usually fired after the de-wax process to remove the residue pattern material, and to improve shell strength through sintering. The firing temperatures are generally high enough to affect the phase constituent and microstructure of the shells, which further influences the shell strength. Firing duration at firing temperature is another important factor having an impact on the shell strength due to grain coarsening, but it is often overlooked by investment foundries. In this article, the room temperature moduli of rupture of investment shells fired at different conditions were determined. The crystallinity of fused silica shells was determined using X-ray diffraction. The differences on the shell strength were discussed and correlated with the microstructure and phase constitution in the shells after different firing processes. [ABSTRACT FROM AUTHOR]

Tree improvement programs on loblolly pine (Pinus taeda) in the southeastern USA has focused primarily on improving growth, form, and disease tolerance. However, due to the recent reduction of design values for visually graded southern yellow pine lumber (including loblolly pine), attention has been drawn to the material quality of genetically improved loblolly pine. In this study, we used the time-of-flight (TOF) acoustic tool to assess the effect of genetic families on diameter, slenderness, fiber length, microfibril angle (MFA), velocity and dynamic stiffness estimated using green density (DMOEG) and basic density (DMOEB) of 14-year-old loblolly pine stands selected from two sites. All the 184 and 204 trees of the selected eight half-sib genetic families on sites 1 and 2 respectively were tested using TOF acoustic tool, and two 5 mm core samples taken at breast height level (1.3 m) used to for the anatomical and physical properties analysis. The results indicated a significant positive linear relationship between dynamic MOEs (DMOEG and DMOEB) versus tree diameter, slenderness, and fiber length while dynamic MOEs negatively but nonsignificant correlated with MFA. While there was no significant difference in DMOEB between sites; velocity2 for site 1 was significantly higher than site 2 but DMOEG was higher for site 2 than site 1. Again, the mean DMOEG and DMOEB reported in the present study presents a snapshot of the expected static MOE for green and 12% moisture conditions respectively for loblolly pine. Furthermore, there were significant differences between families for most of the traits measured and this suggests that forest managers have the opportunity to select families that exhibit the desired fiber morphology for final product performance. Lastly, since the dynamic MOE based on green density (DMOEG), basic density (DMOEB) and velocity2 present difference conclusions, practitioners of this type of acoustic technique should take care when extrapolating results across the sites. [ABSTRACT FROM AUTHOR]

This study deals with the fabrication of three layer hybrid particleboard using kadam branch ( Anthocephalus chinensis ( Lam.) A. Rich ex Walp.) and dhaincha ( Sesbania aculeata ( Willd.)) as raw material with urea formaldehyde resin adhesive as 11% in the face and 9% in the core. Two types of particleboard i.e., dhaincha fine particles: face layer and kadam wood coarse particles:core layer (HB-A) and dhaincha kadam fine mix:face layer and coarse mix:core layer (HB-B) were produced by using three different mixing ratios (50:50, 60:40 and 70:30). Physical and mechanical properties of hybrid particleboards were evaluated according to the procedure of ASTM D-1037 standard. It was found that the particle mixing ratio has a significant effect on the physical and mechanical properties of hybrid particleboards. Consequently, containing lower face layer (30 wt%), the HB-A and HB-B board showed highest density (0.61 and 0.64 g/cm, respectively) as well as MOE (2.56 and 3.56 GPa, respectively) and MOR (18.6 and 26.62 MPa, respectively) among hybrid particleboards. Presence of wood fine particles in face layer also proved effective in properties enhancement. Due to having wood fine particles content in face layer, HB-B type hybrid boards showed higher density and bending strength than HB-A boards. Presence of wood particles in face layer also reduces the WA and TS of the boards. Significant difference was examined among the properties of six particleboards during statistical analysis. The results confirmed that HB-A3 and HB-B3 particleboards met the minimum ANSI A208.1 requirements for physical and mechanical properties of M-3 grade particleboard. In decay resistance test, HB-A type particleboards showed resistance to white rot, but non-resistant for brown rot fungi where the HB-B type particleboards showed moderately resistant to both fungi. So the results indicated that the fabrication HB-B type hybrid particleboards would be technically feasible under lower face layer percentage. [ABSTRACT FROM AUTHOR]

This study was conducted to determine the relation between the dynamic modulus of elasticity and the static modulus of elasticity, and the relation between the dynamic modulus of elasticity and the modulus of rupture of mandarin peel-sawdust composite boards. The result of this study was as follows: There was highly close linear correlation between the dynamic modulus of elasticity and the static modulus of elasticity, modulus of rupture of the mandarin peel-sawdust composite boards with the density of 0.4, 0.5 and 0.6 g/cm, and the mandarin peel content of 10, 20, 30 and 40%, thus, the static modulus of elasticity and the modulus of rupture can be predicted from the dynamic modulus of elasticity measured by free vibration test using resonance frequency. [ABSTRACT FROM AUTHOR]

The Taguchi method was used to determine the optimum content of a four-parameters cellulose fiber pulp, polyvinyl alcohol (PVA) fibers, a silica fume, and bentonite for cement-based composite sheets. Then cement composite sheets from the hybrid of PVA and the cellulose fiber pulp were manufactured, and their moduli of rapture were determined experimentally. The result obtained showed that cement composites with a hybrid of PVA and cellulose fiber pulp had a higher flexural strength than cellulose-fiber- reinforced cement ones, but this strength was rather similar to that of asbestos-fiber-reinforced cement composites. Also, using the results of flexural tests and an analytical method, the tensile and compressive moduli of the hybrid of PVA and cement sheet were calculated. The hybrid of PVA and cellulose fiber pulp is proposed as an appropriate alternative for substituting asbestos in the Hatschek process. [ABSTRACT FROM AUTHOR]

Steel fibre reinforced concrete (SFRC) is an advanced cementitious composite where fibres can act as a profitable replacement for diffused reinforcement, like welded steel mesh, especially for thin cross sections. In this case fire becomes a very important condition in the design. Previous experimental research has shown the benefits in fire resistance of steel fibres, when structural elements are bent. The proper understanding of the effects of elevated temperatures on the properties of SFRC is necessary. In this study, constitutive relationships are developed for high-strength FRSC subjected to fire, with the purpose of given that capable modelling and to specify the fire-performance criteria for concrete structures. They are developed for unconfined FRSC specimens that include compressive and tensile strengths, modulus of elasticity, modulus of rupture, strain at peak stress, and compressive stress-strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish compressive stress-strain relationships. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper the tensile strength of Lightweight Aggregate Concrete (LWAC) produced with different types of expanded clay aggregates is characterized. A comprehensive experimental study was carried out on different concrete compositions with mean compressive strengths from 30 to 70 MPa and density classes from D1.6 to D2.0. The influence on the splitting tensile strength and modulus of rupture of the curing conditions and initial wetting of lightweight aggregate is studied. For concretes of equivalent compressive strength, the tensile strength is almost independent of the type of lightweight aggregate. The tensile strength of LWAC was about 0.8-0.85 of that of Normal Weight Concrete (NWC) of equal strength, decreasing to about 0.7 in LWAC with lightweight sand. Contrary to compressive strength, the LWAC with less porous aggregates has lower tensile structural efficiency than NWC. But the tensile structural efficiency of moist-cured concrete is little affected by the volume and wetting conditions of aggregate. There is a reduction in the splitting strength of air-cured concrete that is not predicted in the normalization and it is greater for NWC than for LWAC. However, the modulus of rupture of air-cured LWAC can only be about 0.5-0.8 of that of NWC of equal strength. [ABSTRACT FROM AUTHOR]

Three different claybinders (Mfensi, Afari, and Fosu clays) were used to improve the plasticity of lithomargic clay. Lithomargic clay binder formulations were produced in a ratio of 4:1 by mixing, moulding, drying and firing at 1350°C for 2 hours. Properties including linear firing shrinkage, bulk density, apparent porosity, water absorption, and cold crushing strength were measured. The modulus of rupture of the fired bricks was measured before and after thermal cycling to evaluate their thermal shock resistance. The results show that the properties of the fired bricks depend strongly on the chemical composition of the clay binders. Mfensi clay exhibited good combination of properties with low water absorption, very good cold crushing strength and thermal shock resistance. [ABSTRACT FROM AUTHOR]

The effect of addition of fly ash and metakaolin as mineral admixtures to M60 grade concrete for making of High Performance Concrete (HPC) and influence of Polyolefin Macro-Monofilament (PMM) fibre on High Performance Concrete was studied in detail. The Polyolefin Macro-Monofilament fibre Reinforced High Performance Concrete (PMMFRHPC) mix, grade M60 concrete was designed as per ACI 211.4R-08 (2008). The investigation was carried out on the control mix, HPC, PMMFRHPC containing PMM fibre at the various dosages of 0.1, 0.2 and 0.3 percentages by the volume fraction of concrete. The strength properties were assessed by conducting compressive, splitting tensile, modulus of rupture and modulus of elasticity test. PMMFRHPC mix FMHP03 showed increase in compressive strength splitting tensile strength and higher modulus of rupture of the order 10%, 25% and 58% at age of 28 days when compared to control mix. Empirical expressions were developed to predict the 28-day compressive strength, splitting tensile strength and modulus of rupture of PMMFRHPC. [ABSTRACT FROM AUTHOR]

Investigations were carried out to study the effect of span depth ratio (span length:thickness) on bending properties viz, modulus of elasticity (MoE) and modulus of rupture (MoR) of plywood. All the three grades of plywood viz. Boiling water proof (BWP), boiling water resistant (BWR) and moisture resistant (MR) were tested and evaluated for MoR and MoE at different span depth ratios of 10:1, 20:1, 32:1 and 48:1 in along the face grain direction and 10:1, 16:1, 20:1 and 24:1 in across the face grain direction, respectively, to study the variation in results because of change in span depth ratio. The results were generalized for all types of plywood viz. MR, BWR and BWP, irrespective of initial raw materials and processing conditions. The results revealed that the bending properties of plywood are in the same range at span depth ratio of greater or equal to 20, whereas reduction of 5-30 % in the values of bending properties was observed for the plywood tested at span depth ratio of 10 as compared to plywood tested at span depth ratio of 20. [ABSTRACT FROM AUTHOR]

Rice hull-sawdust composite boards were manufactured for sound-absorbing boards in construction. The manufacturing parameters were target density (400, 500, 600, and 700 kg/m) and rice hull content as percent weight of rice hull/sawdust/phenol resin (10/80/10, 20/70/10, 30/60/10, and 40/50/10). Commercial gypsum board and fiberboard were also used as comparative sound-absorbing materials. The average modulus of rupture (MOR) of the board with a density of 700 kg/m and rice hull mixing ratio of 10% was 8.6 MPa, and that of the board with a 400 kg/m board density and a rice hull mixing ratio of 40% was 2.2 MPa. The MOR increased with increasing board density or decreasing rice hull mixing ratio. The sound absorption coefficients of some boards (400 kg/m and 10%, 500 kg/m and 30%, and 500 kg/m and 40%) were better than those of the commercial 11-mm-thick gypsum board. Thus, it is concluded that rice hull-sawdust composite boards may be implemented as sound-absorbing barriers in construction due to their high sound absorption coefficients. [ABSTRACT FROM AUTHOR]

The automotive industry has traditionally used ceramic honeycomb substrates as catalyst carriers. The long-term durability of a passenger car's converter is assessed by examining the thermal stresses resulting from the temperature variations experienced under various driving conditions. These thermal stresses constitute the majority of the total stress that the ceramic catalyst substrate experiences while in service. The radial and axial temperature distributions were measured, and the thermal stress was calculated by using the thermal expansion coefficient according to the measured temperature. The threshold stress was determined from the fatigue constant, the required lifetime and the duration of the short term strength tests. The radial temperature variation was higher than the axial temperature variation, and the axial stress was higher than the radial stress because the thermal stress is dependent on the elastic modulus. The radial and axial stresses exist below the threshold thermal stress over the entire engine speed range. [ABSTRACT FROM AUTHOR]

It has been known for several decades that structural and processing parameters can strongly affect the modulus of rupture (MOR) and elasticity (MOE) of particleboards. Several studies that have explored the prediction of MOR and MOE, but to date there is no an accepted model for explaining the effects of structural parameters on these properties. The current study predicts MOR and MOE based on the most important structural parameters: particle size, percentage of adhesive, and density. Three dimensionless groups were created by Buckingham's p-theorem and the MOR and MOE predicted based on a multiple regression model. Moisture content of cake, press time, press temperature, and press pressure were 12%, 5 min, 180°C, and 35 kg/cm, respectively. The results showed that the model developed in this study can predict MOR and MOE with acceptable errors 7.06 and 11.27%, respectively. [ABSTRACT FROM AUTHOR]

The objectives of this study were to establish the method of evaluating wood mechanical properties by acoustic nondestructive testing at standing trees and at logs of a Chinese fi r (Cunninghamia lanceolata (Lamb.) Hook.) plantation, and to compare three acoustic nondestructive methods for evaluating the static bending modulus of elasticity (MOE), modulus of rupture (MOR), and compressive strength parallel-to-grain (σc) of plantation wood as well. Fifteen Chinese fir plantation trees at 36 years of age were selected. Each tree was cut into four logs, for which three values of dynamic modulus of elasticity, i.e., Esw, of the north and south face based on stress waves to assume the measuring state of the standing tree, Efr, longitudinal vibration, and Eus, ultrasonic wave, were measured in the green condition. After log measurements, small specimens were cut and air-dried to 12% moisture content (MC). Static bending tests were then performed to determine the bending MOE and MOR, and compressive tests parallel-to-grain were made to determine σc. The bending MOE of small clear specimens was about 7.1% and 15.4% less than Esw and Eus, respectively, and 11.3% greater than Efr. The differences between the bending MOE and dynamic MOE of logs as determined by the three acoustic methods were statistically significant (P < 0.001). Good correlation (R = 0.77, 0.57, and 0.45) between Esw, Efr, and Eus and static MOE, respectively, were obtained (P < 0.001). It can be concluded that longitudinal vibration may be the most precise and reliable technique to evaluate the mechanical properties of logs among these three acoustic nondestructive methods. Moreover, the results indicate that stress wave technology would be effective to evaluate wood mechanical properties both from logs and from the standing tree. [ABSTRACT FROM AUTHOR]

The dimension lumber (45mm×90mm×3700mm) of plantation Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook.) was graded to four different classes as SS, No.1, No.2 and No.3, according to national lumber grades authority (NLGA) for structure light framing and structure joists and planks. The properties of apparent density was determined at 15% moisture content, bending strength and stiffness were tested according to American Society for Testing and Materials (ASTM) D198-99, and dynamic modulus of elasticity (Eusw) was measured by ultrasonic technique, for predicting the flexural properties of different grade lumbers. The results showed that Eusw was larger than the static MOE. The relationship between Eusw and static MOE was significant at 0.01 level, and the determination coefficients (R2) of the four grade lumbers followed the sequence as R2 No.2 (0.616)> R2 SS (0.567)> R2 No.1 (0.366)> R2 No.3 (0.137). The R2 of Eusw and MOR were lower than that of the Etru and MOR for each grade. The Eusw of all the grade lumbers, except No.3-grade, had significant correlation with the static MOE and MOR, thus the bending strength of those grade lumbers can be estimated by the Eusw. The Etru values of four grade lumbers followed a sequence as No.2-grade (10.701 GPa) > SS-grade (10.359 GPa) > No.1-grade (9.840 GPa) > No.3-grade (9.554 GPa). For the same grade dimension lumber, its Eusw value was larger than static MOE. Mean values of MOR for four grade lumbers follow a sequence as No.2-grade (48.67 MPa) > SS-grade (48.16 MPa) > No.3-grade (46.55 MPa) > No.1-grade (43.39MPa). [ABSTRACT FROM AUTHOR]

An optimum method for producing Al-SiC metal matrix composites was developed by determining the optimum conditions for wetting SiC by aluminum and the optimum parameters for pressureless infiltration of SiC preforms. The quantitative effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys was investigated using the sessile drop technique. The contribution of each of these parameters and their interactions, in terms of a relative power, to the contact angle, surface tension, and driving force for wetting were determined. In addition, an optimized process for enhanced wetting was suggested and validated. The optimum conditions for wetting SiC by aluminum that were arrived at were used to infiltrate SiC preforms and the mechanical properties of the resulting metal matrix composites were measured. The effect of SiC particle size, infiltration time, preform height, vol.% SiC in the preform, and Si coating on the SiC particles on the pressureless infiltration of SiC compacts with aluminum was investigated and quantified. The contribution of each of these parameters and their interactions to the retained porosity in the composite, the modulus of elasticity, and the modulus of rupture were determined. Under optimum infiltration conditions, metal matrix composites with less than 3% porosity, over 200 GPa modulus of elasticity, and about 300 MPa modulus of rupture were routinely produced. [ABSTRACT FROM AUTHOR]

Laboratory studies were conducted to evaluate the effects of drying on soil strength and corn emergence ( Zea mays L.). Corn was germinated in Billings silty clay under a bank of heat lamps which operated 9, 14, 19, or 24 h per day. Soil strength (modules of rupture), soil moisture content and emergence were measured daily. The relationship of soil strength to corn seedling emergence as influenced by the four light and heat durations and bare and mulched soil surfaces was determined. As soil strength increased emergence decreased until it ceased at soil strengths of about 80 kPa. Strength of this soil had a high negative correlation with soil water content and increased with time. Mulching decreased initial rate of drying, decreased crust strength, and improved corn emergence. The 14-hour light and heat treatment resulted in the highest corn emergence. [ABSTRACT FROM AUTHOR]

The adherence of soil particles into stable aggregates increases with the addition of monosaccharides or polysaccharde polymers to soil, either as plant residues, microbial metabolites, or as simple carbohydrates. Microbial polysaccharides are one of the most effective organic agents that promote soil aggregate stability, but the effectiveness of these polymers in stabilizing soil particles varies dramatically between microbial strains, the amount present and the prevailing environmental conditions. We conducted glasshouse and laboratory studies to determine the effectiveness of selected microbial polymers in stabilizing soil aggregates. The addition and thorough mixing of 1.0 mg microbial polymer C g soil of seven bacteria strains ( Arthrobacter viscocus, Azotobacter indicus, Bacillus subtilus, Chromobacterium violaceum, Pseudomonas aeruginosa, Pseudomonas strain I, and Pseudomonas strain II), three deuteromycete strains ( Cryptococcus laurentii, Hansenula holstii, and Mucor rouxii), and two reference compounds (hydroxyethyl guar and glucose) to an Arlington coarse-loamy soil resulted in stimulated soil respiration, increased aggregate stability, and decreased soil bulk density and modulus of rupture when incubated from 1 to 12 weeks. The monosaccharides present in the added polymers were rapidly decomposed and the sacchride content of the polymer-treated soil returned to the level of the soil control (with no polymer addition) after 2 weeks of incubation, while the maximum increase in soil aggregate stability was noted during the 3rd and 4th weeks of incubation. Statistical analyses showed that the glucose content of the polymers added was significantly correlated with soil aggregation [weeks 1 ( r=0.78) and 2 ( r=0.61)], but the extractable soil saccharides were not significantly correlated with increased aggregate stability or decreased soil bulk density during this study. When microbial extracellular polymers were added to soil only a transient increase in soil stability was measured upon decomposition of the added saccharides. This finding suggests that the stabilization of soil aggregates is a result of other microbial processes or metabolites rather than the direct binding effects of the added polysaccharides. [ABSTRACT FROM AUTHOR]

Possible tradeoffs between efficiency of water transport and mechanical strength were examined in stems of two congeneric pairs of co-occurring chaparral shrubs. First, since previously published results indicated that Adenostoma sparsifolium (Rosaceae) had greater specific conductivity ( ks or hydraulic conductivity per xylem transverse area) than A. fasciculatum, it was hypothesized that A. sparsifolium would have greater vessel lumen area per square millimeter of xylem area, and less mechanical strength, than A. fasciculatum. Secondly, since Ceanothus megacarpus (Rhamnaceae) is a non-sprouter (unable to sprout from the root crown following fire or other major disturbance) whereas C. spinosus is a sprouter and thus able to form new stems following disturbance, it was hypothesized that C. megacarpus would have greater mechanical strength, but lower ks, than C. spinosus. Both hypotheses were supported. Based upon computer-aided image analyses, A. sparsifolum had significantly higher mean and maximum vessel diameters (16.4, 40.5 vs. 14.6, 35.7 μm), a 34% greater percent vessel lumen area, and a two-fold greater measured and theoretical ks than A. fasciculatum. This corresponded to 14% lower stem density (wet weight/volume) and less mechanical strength, with a 37% lower modulus of elasticity (MOE) and a 30% lower modulus of rupture (MOR) than A. fasciculatum. Similarly, C.␣spinosus had a significantly higher maximum vessel diameter (52.7 vs. 41.8 μm) and a 92% higher theoretical ks (and 43% higher measured ks) than C. megacarpus. This corresponded to a 9% lower stem density and 20% lower MOR than for C. megacarpus. Thus, at least within these two congeneric pairs of chaparral shrubs growing together in the same habitat, there may be tradeoffs between mechanical strength and conductive efficiency of the stem xylem which correspond to differences in transport physiology and life history traits of sprouter versus non-sprouter species. [ABSTRACT FROM AUTHOR]

The quality of dimension lumber (2 by 4 lumber) was preliminarily investigated in four common Mongolian softwoods: Pinus sylvestris L., Pinus sibirica Du Tour, Picea obovata Ledeb., and Larix sibirica Ledeb. to produce high quality dimension lumber for structural use. In total 61, 39, 67, and 37 pieces of lumber were prepared for Pinus sylvestris, Pinus sibirica, Picea obovata, and L. sibirica, respectively. The lumber was visually graded and then tested in static bending to obtain the 5% lower tolerance limits at 75% confidence level (f0.05) of the modulus of elasticity (MOE) and the modulus of rupture (MOR). In addition, the effects of sawing patterns on bending properties were also analyzed. The f0.05 of the MOE and MOR were 4.75 GPa and 15.6 MPa, 3.39 GPa and 11.0 MPa, 3.78 GPa and 11.7 MPa, and 6.07 GPa and 22.3 MPa for Pinus sylvestris, Pinus sibirica, Picea obovata, and L. sibirica, respectively. These results suggested that with a few exceptions, characteristic values of MOR in the four common Mongolian softwoods resembled those in similar commercial species already used. In visual grading, over 80% of total lumber was assigned to select structural and No. 1 grades in Pinus sylvestris and Pinus sibirica, whereas approximately 40% of total lumber in L. sibirica was No. 3 and out of grades. Sawing patterns affected bending properties in Pinus sylvestris and L. sibirica, but did not affect Pinus sibirica and Picea obovata. Dynamic Young's modulus was significantly correlated with bending properties of dimension lumber for the four species. Based on the results, it was concluded that dimension lumber for structural use can be produced from the four common Mongolian softwoods. [ABSTRACT FROM AUTHOR]