Durability Index Research Articles

Advances in Understanding the Mechanism of Ophthalmic Viscosurgical Device Retention in the Anterior Chamber or on the Corneal Surface during Ocular Surgery.

Retention durability, especially in the eye, is one of the most important properties of ophthalmic viscosurgical devices (OVDs) during ocular surgery. However, the information on the physical properties of OVDs is insufficient to explain their retention durability. The purpose of this study is to clarify the mechanism of OVD retention to improve understanding of the behavior of OVDs during ocular surgery. To elucidate the mechanism of OVD retention, we have developed a new test method for measuring repulsive force. As a result, the maximum repulsive force of OVDs was positively and well correlated with the retention durability of investigated OVDs. Consequently, we demonstrated that the repulsive force could be used as an index of retention durability on the ocular surface and in the eye. We directly compared the intraocular retention durability of three OVDs (Shellgan, Viscoat, and Opegan-Hi) in ex vivo porcine eyes. Opegan-Hi was immediately removed from the anterior chamber, but Shellgan and Viscoat remained largely in the anterior chamber as determined by fluorescence imaging. These results showed that the intraocular retention behavior of OVDs was similar to their ocular surface behavior in our previous report, suggesting that retention durability is dependent on the OVD itself. The retention durability of Shellgan seemed to be higher than that of Viscoat, and the maximum repulsive force of Shellgan was 1.35-fold higher than that of Viscoat. Therefore, the repulsive force might be a useful index for assessing the difference in the retention durability between OVDs such as Shellgan and Viscoat.

Relationship between pellet durability index and hardness of pellet with various binder for broiler finisher phase

Feed quality is not only in terms of nutrition but also from physical quality. Good physical quality will increase feed consumption and improve the performance of broilers finisher phase. One feed that is usually given is pellets. This research aims to determine the effect of using molasses, tapioca flour and bentonite binder on relationship between pellet durability index and hardness of pellet for broiler finisher phase. The experimental design used was a completely randomized design with 4 treatments and 4 replications. The treatments were feed of broiler finisher phase with the addition of binder, as follows: P0 (without binder); P1 (molasses 2%); P2 (tapioca flour 2%) and P3 (bentonite 2%). To determine the relationship between pellet durability index (Y) and hardness (X) using simple linear regression analysis. The research results showed that the pellet durability index is strongly influenced by the level of pellet hardness where the higher hardness value will increase pellet durability index, with a correlation of 79.80%.

Determining the relationship between shear wave velocity and physicomechanical properties of rocks

Thorough knowledge of physicomechanical properties of rocks is crucial during the primary and secondary stages of designing a rock engineering project. Laboratory examination of these properties requires high-quality rock specimens. However, preparing such high accuracy samples is a difficult, expensive, and time-consuming task, especially in weak and fractured rocks. Hence, indirect approaches seem an attractive research area for determining these properties. The main object of this study is to develop some empirical relations to determine different physical and mechanical properties of sedimentary and metamorphic rocks based on the shear wave velocity index. To do that, several schist, phyllite, and sandstone core samples were collected from the drilled boreholes in the Marivan Azad dam in western Iran. Then, the shear wave velocity and some physical and mechanical properties of rocks were measured in dry and saturated conditions. Subsequently, statistical analyses were conducted to develop shear wave velocity-based equations to determine different rock properties, including uniaxial compressive strength, modulus of elasticity, porosity, Poisson’s ratio, slake durability index, density, and water absorption. An equation with the maximum correlation coefficient was proposed as the optimum equation to determine each of the above rock properties. Finally, the results of the proposed empirical equations were compared with those of laboratory measurements. This comparison proved the proposed equations to have high accuracy for determining the physicomechanical properties of rocks and can be used in practical projects with similar geological conditions to save time and money.

Predicting slake durability of carbonate rocks using geomechanical properties (Case study: Durood-Khorramabad highway, Iran)

This study investigates the relationship between slake durability indices and geomechanical characteristics of five types of carbonate rocks situated in the west of Iran along the Doruod-Khorramabad highway. In this study, five types of limestone rocks were selected, including grey limestone (A), marly limestone (B, C, D), and sandy limestone (E). The geomechanical characteristics of the studied limestones were calculated based on the ISRM (1981) standard stimulations. Statistical approaches were executed to find the most influential geomechanical characteristics on slake durability indices and to find an appropriate slake durability cycle for interpreting rock behaviors. According to the simple regression analysis, the first and fourth cycles of slake durability can provide adequately good information for initial engineering/design works. Also, the correlation coefficients demonstrated nearly constant change after the fourth cycle. Geomechanical parameters, like Schmidt hammer and dry density, showed the highest correlation with the fourth slake durability cycle (R =0.98). On the other hand, uniaxial compressive strength revealed a poor correlation (R = 0.49) with this cycle. Apart from estimating the 4th durability cycle from geomechanical properties, it is possible to calculate the second to fourth cycles of slake durability using the results of the first durability cycle (R = 0.99–0.94). Consequently, a multivariate equation was developed based on water absorption, Schmidt hammer, effective porosity, and modulus of elasticity with R2=0.89 using the best subset regression method.

Assessment of durability and deterioration of rocks from western Iraq

The behavior of rocks in water can be expressed in terms of their ability to resist slaking when exposed to water. This ability to withstand durability and deterioration from weathering affects both the effectiveness of the engineering project and its cost. Durability and deterioration of rock from the west of Iraq are little studied, and there is little confidence in these properties to be utilized in engineering works. This study is emphasized on the information obtained from the slaking durability test, specific gravity, and absorption tests performed to evaluate durability and deterioration properties of the rock samples taken from the stratum of the Rutba-Jezira Zone, western Iraq. An examination of the statistical relationship between water content, slake durability index, specific gravities and absorption was also included. The results show that the durability and deterioration of the investigated rock are variable due to the occurrences of a different secondary constituent. Such rock can deteriorate rapidly upon exposure or slake and soften when in contact with water. As a result, the rock of the study area is problem material in several phases of geotechnical engineering.

The effect of raw material moisture and particle size on agri-pellet production parameters and physical properties: A case study for greenhouse melon residues

There are many agricultural residues that can be considered as biomass raw materials according to the region where it grows. Due to the physical and chemical diversity of agricultural residues, pelleting conditions and pellet properties need to be determined for effective use. Aim of this study is to determine the pelletizing conditions and pellet properties of melon stalks from greenhouse residues that can be biomass raw materials. In this study, the stalks obtained after harvest operations in greenhouse melon cultivation were milled with two different sieve hole diameters as 4 mm (M4) and 6 mm (M6). The ground material was pelleted at two moisture content, 10% (M4-10; M6-10) and 15% (M4-15; M6-15). During the pelletizing process, the highest pellet production capacity (103.86 kg/h) and the lowest specific energy consumption (73.92 kWh/ton) were obtained in M4-15 pellets. Regarding pellet physical properties, the effect of pelletizing moisture on pellet moisture content, bulk density, single pellet density and durability index were statistically significant, while particle size only affected the bulk density (p < 0.05). Pelletizing moisture caused a decrease in durability index and bulk density for both particle sizes. At the end of the study, it was observed that the melon stalk pellets met ENplus pellet standards in terms of pellet moisture, bulk density and durability. Although the pelletizing process is easy and efficient, the high ash content (20.73%) and low calorific value (11.92 MJ/kg) of melon stalks may prevent it from being used as solid fuel in domestic heating systems.

Durability Performance Indices for Cement-Based Mortars.

Corrosion-induced damaged structures are generally repaired using locally available materials. Nevertheless, determining the durability of the repair materials to be used is necessary to forecast its service life after being placed on the damaged structure. In previous investigations, the most commonly used durability indices are saturated electrical resistivity (ρS), ultrasonic pulse velocity (UPV), total void content (TVC), water capillary absorption (WCA), rapid chloride permeability (RCP), and compressive strength (fc). Four repair mortar types were evaluated. For each mortar type, 5 × 5 cm2 cubes, 5 × 10 cm2 (small) cylinders, and 10 × 20 cm2 (large) cylinders were made from each mortar evaluated. On the basis of the present results, the durability design of mortars should consider not only the mechanical strength, but also the durability index values to define its durability performance. According to the empirical correlations obtained between all durability indices, ρS vs. RCP, TVC vs. WCA, and RCP vs. WCA were the ones with higher correlation coefficient. These correlations could be used for mortar mixture durability forecasting.

Slaking behavior of evaporitic rocks from Abu Dhabi area, United Arab Emirates

Slaking behavior of rocks is an essential indicator of their ability to resist degradation and is commonly assessed via the second cycle of slake durability index (Id2, SDI) test. In Abu Dhabi area, the evaporitic rocks commonly extend from the near surface to several meters depth, so that they lie at the foundation level of buildings and other infrastructures. Evaporites pose significant challenges for the construction sectors due to the easily degradable nature of these rocks. This study presents new and definitive data for evaporites that provides essential information for the construction businesses, engineers, and decision makers. Eighty-six rock blocks from eleven locations were collected. A representative sample of each block was extracted for slake durability testing. Samples were prepared and tested according to ASTM standards. Before and after the slaking process, the mineralogical composition and characteristic textures of the samples were examined in petrographic thin section and via XRD (X-ray diffraction), XRF (X-ray fluorescence), and SEM (scanning electron microscopy) analyses. Based on multiple cycling, Id1 to Id4, the slake test data for evaporitic rocks from Abu Dhabi indicate high to very low values. The weight loss values from the first to the fourth cycle (Id1–Id4) of all samples lie in the range 40 to 93 wt%. This is attributed to chemical and mineralogical properties of the evaporites, which allow rapid development of hydration-dehydration effects. The evaluation of the slaking behavior of evaporitic rocks provides explanations for durability problems associated with these rocks in the study area and elsewhere.

Effect of binding materials on physical and fuel characteristics of bagasse based pellets

Growing energy demand and environmental issues are demanding the use of biomass based energy generation processes. However, inherent low bulk density of biomass poses problems of handling, storage and transportation which hinders its large scale application and demands its pretreatment. Pelletization process can address this inherent issue of biomass by converting it into a dense pellet having a regular shape and size. The strength of raw biomass pellet is very low and requires the use of binders. Therefore, in this study, cow dung and molasses were used as binders for the formation of bagasse based pellets. The effects of operating parameters, biomass composition, molasses concentration and drying time, on the physical and fuel characteristics of the pellets were studied and the response was recorded in terms of bulk density, pellet density, durability index, calorific value and proximate analysis. Based on experimental results, a significant trade off between durability index and calorific values of the pellets was observed and thus, the optimization of operating parameters was carried out. At optimal conditions, the pellet has the calorific value of 16.43 MJ kg−1 with 84.2% durability index. Subsequently, torrefaction of biomass was performed to upgrade the energy quality of the pellets. Thermal treatment resulted in 10% improvement in energy content of the biomass and also raised the durability of the pellet slightly. Moreover, the application of cow dung as a binder can be considered as a sustainable approach to improve the physical and fuel properties especially durability index of the pellets. Thus, these durable pellets can be used as a fuel in energy generation processes and for heating purposes in rural regions.

PSII-17 Phosphorus Release Values in Growing Pigs Fed Increments of Optiphos Plus Phytase in Pelleted Diets

Abstract The efficacy of phytase (Pase) from OptiPhos Plus G (Huvepharma, Peachtree City, GA) was compared to inorganic phosphorus (iP) supplements to assess phosphorus equivalency. In 6 replicate 28-d trials, 288 crossbred F2 (Duroc X LR X LW) pigs (20.0 kg, 6 pigs/pen, 48 pens) were randomly assigned to 1 of 8 diets. Pig sex was balanced within pens. Basal corn-soybean meal diets, formulated to exceed nutrient requirements except for Ca and P, supplied 1.30% lysine from the same amounts of all ingredients. Sand was used to balance variable amounts of monocalcium phosphate and limestone. Diets supplied either 0.061, 0.156, or 0.241% iP from monocalcium phosphate or increments of 250, 500, 750, 1,000 and 1,500 FTU/kg from Pase. All diets were pelleted (160°F, 2.5 tons/hr). The modified pellet durability index averaged 92.8% and 88.7% for all diets in each of 2 mixes. Non-linear growth responses to increments of iP and Pase were detected (P &amp;lt; 0.05). Using nonlinear regression models, maximum gain was calculated at 0.23% iP and 1144 FTU/kg Pase (equivalent to 0.31% available P or 0.38% STTD P). Likewise, from non-linear responses (P &amp;lt; 0.05), maximum response in whole-body bone mineral content (WBBMC) from analysis of dual energy x-ray absorptiometry scans were calculated at 1227 FTU/kg Pase. The maximum Pase response for WBBMC was below expectations and raised concerns for potential Ca limitations in diets at higher Pase supplements. Only linear WBBMC responses (P &amp;lt; 0.001) to iP levels were detected. Responses across iP and Pase treatments for femur bone mineral content reflected the same conclusions as responses to WBBMC. As growth responses to iP and Pase diets were non-linear, simple conversions of phytase activity to phosphorus release was not straight-forward. However, non-linear equations can predict economic values of target levels as a function of ingredient costs.

Physio-Mechanical Characterization of Rocks

Abstract The present study aims to investigate the physical, petrological, and mechanical properties of ten different types of rocks in the Indian subcontinent, required for the design of structures built in rocks. A comparative assessment is done for the stress-strain response of all the rocks collected under three main categories, e.g., igneous, sedimentary, and metamorphic. The physical properties, e.g., densities and slake durability indices, are determined. The peterological tests are carried out by scanning electron microscope and the X-ray diffraction technique. Mechanical properties, e.g., hardness, uniaxial compressive strength, elastic modulus, and Poisson’s ratio, of the 10 different types of rocks are obtained through static loading at a strain rate of 0.001/s. Lastly, various correlation equations are proposed relating the uniaxial compressive strength, density, elastic modulus, and hardness of the 10 rocks. And the rocks are classified based on the Deere-Miller rock mass classification system.

Effect of whole-grain rice on pellet quality, geese performance, and economic benefits

This study evaluated the effects of whole-grain rice ( WGR ) on pellet quality, geese performance, and economic benefits. A total of 360 one-day-old healthy male Jiangnan White goslings with similar body weight ( BW ) were randomly divided into 2 groups with 6 replicates per group and 30 geese per replicate. Pelleted diets were prepared with WGR for the experimental group and crushed rice ( CR ) for the control group to create the 2 treatments. Dietary rice (unhusked) inclusions were 20% for 1 to 21 d and 40% for 22 to 70 d. The pellets from d 1 to 21 were crumbled. Prepelleted WGR significantly decreased pellet length, hardness and pellet durability index. WGR pellets had significantly higher fine ratio (≤2.8 mm) and starch gelatinization than CR pellets. The different treatments did not affect BW on 21, 42, and 70 d of age or average daily feed intake ( ADFI ), average daily gain, and feed to gain ratio (F/G) from 1 to 70 d. However, compared with the CR diet, the WGR diet increased ADFI and F/G from 1 to 21 d. At 70 d of age, similar slaughter performance, relative viscera weight, and meat quality of geese were observed, except for a significant increase in the spleen ratio in the WGR treatment compared with the CR treatment. From the observation, pelleting with WGR reduced the cost of feed manufacture by decreasing the electricity use of grinding and had no negative effect on feed cost per/kg weight gain of geese. Even with the decreased pellet quality, we recommend replacing CR in geese diets with WGR from 22 to 70 d of age in view of the geese performance, economic benefits, and electricity savings.

The study of split mastic asphalt pavement with latex addition for flooded road

This study aims to determine the effect of latex addition to the durability of the Split Mastic Asphalt (SMA) pavement mixture in order to increase its durability when the road is flooded. Durability test conducted where the sample was immersed in water for 0, 24, 48, 72, 96 hours, with latex variations of 1.5%, 2%, 2.5%, 3%, 3.5%. From the results of the study it was found that the durability of asphalt mixture without latex was higher than that of SMA with latex. The durability indexes were 6.740%, 10.648, 11.717, 13.884, 14.766 and 9.991 for 0%, 1.5%, 2%, 2.5%, 3%, 3.5% latex in the mixture respectively. The higher the index the lower the strength. In addition, the longer the soaking time the lower the strength. However, as the latex in the mixture increases, the stability was also increase achieved at 3% latex. The SMA pavement mixture with the addition of latex does not increase its durability but can increase its stability value. So, it is recommended that SMA pavement mixture with latex is only for pavement where the water level is not high.

Pirinanın farklı nem içeriklerinde peletlenmesi işleminin peletlerin fiziksel özellikleri üzerine etkileri

Bu çalışmada, zeytinyağı üretimi sırasında yan ürün olarak ortaya çıkan pirina üç farklı nem içeriğinde (%14, %17 ve %20) peletlenmiş ve farklı nem içeriklerinin peletlerin fiziksel kalite değerleri üzerine etkisi araştırılmıştır. Nem içeriği değişkenine bağlı olarak pelet üretim koşulları ile ilgili üretim kapasitesi ve özgül enerji tüketimi değerleri belirlenmiştir. Pelet fiziksel özellikleriyle ilgili nem içeriği, parça yoğunluğu, yığın yoğunluğu, dayanıklılık direnci ve sıkıştırma direnci testleri yapılmıştır. Çalışma sonunda en yüksek üretim kapasitesi ve en düşük özgül enerji tüketimi sırasıyla 225.59 kg h-1 ve 45.13 kWh ton-1 ile %20 nem içeriğine sahip pirinada elde edilmiştir. Yüksek nem içeriğinde pelet üretiminin daha kolay gerçekleştiği ve daha az enerji gerektirdiği belirlenmiştir. Peletleme işleminde nem düzeyi artışının, parça yoğunluğu ve yığın yoğunluğu değişimine etkisi istatistiksel açıdan önemsiz bulunmuştur. Pelet dayanıklılık direnci peletleme neminin artmasıyla artış göstermiş, en yüksek dayanıklılık direnci %20 nem içeriğindeki peletleme işleminde %70 olarak hesaplanmıştır. Elde edilen peletlerin nem içeriği, yığın yoğunluğu ve dayanıklılık direnci değerleri EnPlus pelet standartlarını karşılamamaktadır. Her üç nem içeriğinde üretilen peletlerin dayanıklı yapıda olmadığı saptanmıştır. Pirina içerisinde bulunan zeytin çekirdeği parçalarının, pirinanın pelet formasyonu kazanması ve dayanıklı yapıda kalmasını engellediği sonucuna varılmıştır.

Petrological control on engineering properties of carbonate rocks in arid regions

Petrological features of carbonate rocks that exert control on their mechanical and physical properties are examined in the study presented here. Ninety-four representative rock block samples were collected at outcrops and were tested for uniaxial compressive strength (UCS), point load index (PLI), indirect tensile strength (ITS), sonic velocity (SV; Vp and Vs), Schmidt hardness value (SHV), slake durability index (SDI), porosity (n), water absorption (WA), unit weight (UW), and specific gravity (SG), according to the standards. The carbonate rock samples were classified into four groups, according to their compositional and textural characteristics, using XRD, XRF, polarized-light microscope, and SEM. Different types of regression analyses were performed to find the most applicable relationship between measured mechanical/physical properties and mineralogical/textural features of these carbonate rocks. The results suggest that rocks with pure calcite (no dolomite component) and abundant iron oxide cement are more sensitive to mechanical failure than the other carbonate rocks tested here. High silica content appears to reduce the UCS and Id2 values probably due to the presence of silica as separate chert nodules and detrital quartz grains. The results also suggest impact of the arid environmental conditions in the study area. The correlation data indicated wide range of variability and cover ranges reported in published literature on carbonate rocks from other regions. The derived correlation equations of the rock strength parameters may be specific within the arid environment of the investigated rocks, but the results may still provide comparative guidelines for rock testing in the region and regions of other carbonate rocks.

A new durability assessment method of the tuffs used in some historical buildings of Cappadocia (Turkey)

Cappadocia region in Turkey is known as a touristic and historical area with volcanic rocks formed by the effect of intense Neogene calcalkaline volcanism. Rhyolitic to trachyandesitic tuffs, being widespread as a volcanic rock in this region, are used as building stone in historical structures and many monuments with cultural heritage. However, since they have variable durability performances, it is important to evaluate the durability of tuffs for restoration purposes. The aim of this study is to characterize the tuffs using their properties including effective porosity, water absorption, dry and saturated unit weights, dry and saturated uniaxial compressive strengths, dry and saturated point load strengths, dry and saturated sonic velocities and slake durability index, and to estimate the long-term durability of tuffs based on the correlation between field performances and measured properties of the tuffs. In the context of this study, 13 tuff samples used in ancient monuments with good durability performances were taken from nine quarries of Kayseri and Aksaray areas in the Cappadocia region. The physical and mechanical properties of these tuffs were investigated. The properties of these tuffs and the ones with poor durability based on the literature data were compared. A series of correlation graphs using unit weight, effective porosity, water absorption, sonic velocity, and uniaxial compressive strength values of all tuffs has been developed to identify durable and non-durable tuffs. Among these, effective porosity (by volume)-dry sonic velocity and effective porosity (by volume)-dry uniaxial compressive strength pairs yield better durability assessment for the tuffs.

Evaluation of mechanical strength and physical properties of indurated laterite with regard to in situ characterization of lateritic profile

The majority of the geotechnical studies on lateritic materials in different parts of the world including India was carried out from the viewpoint of soil characterization and was not particularly meant for indurated laterites. With due need, in this study, mechanical strength and physical properties of indurated laterites from an abandoned quarry of Kharagpur (India) were investigated with regard to in situ characterization of the lateritic profile. Based on texture, appearance and relative strength of the lateritic materials, a total of four horizontal/sub-horizontal zones (Zones 1–4) sequentially lying below a thin humus zone existing on the top of the profile were identified. The indurated laterites were found to be confined within Zones 1 and 2 and were used to determine uniaxial compressive, point load and Brazilian tensile strengths; effective porosity; dry density; vug volumetric percentage (a newly introduced index); and slake durability indices by adopting a modified methodology. The pattern of variation of all these parameters with regard to the sample depth was found to be broadly in agreement with the in situ characteristics of the laterite profile. The quality of the indurated laterites for construction purposes was also assessed. The point load strength proved to be the most useful/practical strength parameter in characterizing indurated laterites. Both vug volumetric percentage and slake durability indices were found to be much more efficient than effective porosity and dry density in estimating the point load strength. The reasons behind all important observations are also elucidated in this paper.

Acid rain: an unsuspected factor predisposing Panzhihua airport landslide, China.

Understanding the effect of acid rain to landslides is crucial for a better landslide risk assessment. This work aims to reveal the unsuspected but key role of acid rain in Panzhihua airport landslide, China. Firstly, we propose a hypothesis that acid rain may aggravate the slaking behavior of mudstone at weak interlayer and make it more fragmented, eventually further reducing its shear strength and predisposing the Panzhihua airport landslide. Subsequently, mudstone samples are subjected to slaking durability test, respectively, using water with a pH of 7 and two dilute hydrochloric acid solution with pH of 5 and 3. Slaking durability index (Idn) is adopted aiming to quantitatively evaluate the impact of acid rain on the slaking. Moreover, the mechanisms of acid rain affecting the slaking behavior of mudstone are revealed by (1) analyzing cation compositions changes in different pH slaking fluid and (2) observing micro-structure change of mudstone-chip before and after acid rain treatment. Finally, three works are conducted as evidences to prove that acid rain indeed plays a key role in the occurrence of Panzhihua airport landslide, including (1) analysis of the link between the slaking behavior of mudstone and its shear strength, (2) comparison of cations between spring water at the edge of the toe of landslide and acid rain, and (3) comparison of mineral contents of mudstone samples collected from different locations. These findings have implications for comprehensively analyzing the formation mechanism of landslide in acid rain area (such as Europe, North America, and China).

Factors Contributing to Landslide Susceptibility of the Kope Formation, Cincinnati, Ohio

ABSTRACT The objective of this study was to evaluate the factors that contribute to the high frequency of landslides in the Kope Formation and the overlying colluvial soil present in the Cincinnati area, southwestern Ohio. The Kope Formation consists of approximately 80 percent shale inter-bedded with 20 percent limestone. The colluvium that forms from the weathering of the shale bedrock consists of a low-plasticity clay. Based on field observations, LiDAR data, and information gathered from city and county agencies, we created a landslide inventory map for the Cincinnati area, identifying 842 landslides. From the inventory map, we selected 10 landslides that included seven rotational and three translational slides for detailed investigations. Representative samples were collected from the landslide sites for determining natural water content, Atterberg limits, grain size distribution, shear strength parameters, and slake durability index. For the translational landslides, strength parameters were determined along the contact between the bedrock and the overlying colluvium. The results of the study indicate that multiple factors contribute to landslide susceptibility of the Kope Formation and the overlying colluvium, including low shear strength of the colluvial soil, development of porewater pressure within the slope, human activity such as loading the top or cutting the toe of a slope, low to very low durability of the bedrock that allows rapid disintegration of the bedrock and accumulation of colluvial soil, undercutting of the slope toe by stream water, and steepness of the slopes.

Effects of conditioning temperature and pellet mill die speed on pellet quality and relative stabilities of phytase and xylanase.

The objective of this experiment was to determine the effect of conditioning temperature and die speed on pellet quality and enzyme stability of phytase and xylanase. Treatments were initially arranged as a 2 × 3 factorial of conditioning temperature (74 and 85 °C) and die speed (127, 190, and 254 rpm); however, when conditioning at 85 °C, it was not possible to pellet at 127 rpm. Thus, data were analyzed in two different segments using the GLIMMIX procedure of SAS. First, linear and quadratic contrasts were utilized to test the response to increasing die speed at 74 °C. Second, the data was analyzed as a 2 × 2 factorial of conditioning temperature (74 and 85 °C) and die speed (190 and 254 rpm). Treatments were arranged in a completely randomized design and replicated three times. Diets were conditioned for approximately 30 s and pelleted with a 4.8-mm-diameter × 44.5-mm-effective length die at a rate of 4.5 MT/h. Pellet durability index (PDI) was determined using the tumble box and Holmen NHP 100 methods. Samples of the unconditioned mash (M), conditioned mash (CM), and pellets (P) were collected and analyzed for phytase and xylanase concentration. Relative enzyme stabilities were expressed as CM:M, P:CM, and P:M. Stabilities expressed as P:M were used an indication of enzyme stability through the entire pelleting process. Diets conditioned at 74 °C showed no evidence of difference in phytase or xylanase P:M stability when decreasing die speed from 254 to 127 rpm. However, when conditioning diets at 74 °C, decreasing die speed increased (linear, P < 0.001) PDI. There was no conditioning temperature × die speed interaction for overall xylanase P:M stability or PDI. However, there was a conditioning temperature × die speed interaction (P < 0.01) for phytase P:M stability. When conditioning diets at 85 °C, increasing die speed decreased phytase P:M stability. However, when conditioning at 74 °C, increasing die speed did not influence phytase P:M stability. For main effects of conditioning temperature, increasing temperature improved (P < 0.001) PDI with no evidence of difference for xylanase P:M stability. For the main effects of die speed (254 vs. 190 rpm), decreasing die speed decreased (P < 0.001) the P:M xylanase stability, but there was no evidence of difference for PDI. The results of this trial indicate that die speed should be taken into consideration when evaluating enzyme stability of both phytase and xylanase as pellet mill models may be operating at different speeds. Additionally, increasing conditioning temperature will improve PDI but may result in decreased phytase stability.