Reduction In Total Porosity Research Articles

Minimum cement content requirements: a must or a myth?

The objective of the present work was to systematically investigate the issue of minimum cement content requirements, by studying the behavior of concretes with different water to cement ratios ( w/c) in the range of 0.45–0.70, in which the cement content was varied, by controlling the water content, using water reducing admixtures. The effect of cement content was noted to be different for various properties: strength was a function of w/c and independent of cement content; total water absorption was proportional to the paste content at a given w/c, while capillary absorption and chloride ingress reduced with a reduction in the cement content for a given w/c, to an extent which was much greater than the reduction in total porosity. Carbonation and shrinkage were largely independent of cement content for a given w/c. The trends observed were discussed in terms of the effect of paste content on concrete properties, and the influence of admixtures on the paste properties. These results suggest that requirements for minimum cement content in standards should be revisited.

Soil faunal activity of an oil-polluted tropical alfisol amended with organic wastes as determined by micromorphological observations

This study evaluates the effect of used-lubricating oil (spent oil) and organic nutrient supplements as derived from animal droppings on faunal activity as expressed in the incidence of faunal excrement and related micromorphological features. This approach allows the effects of the treatments to be evaluated even if the organisms are no longer present. The main-plot treatments included control (C), cow dung (CD), poultry droppings or manure (PM) and pig droppings or waste (PW) each at 10 Mg ha −1 each. The sub-plot treatments were control (no applied contaminant), 0.5%, 2.5% and 5% spent oil (SP) applied at 10, 50 and 100 Mg ha −1 (w/w), respectively. Residual oil blobs were clear in soil thin sections and the results from point counting demonstrated a significant reduction in oil content following the addition of organic wastes to the polluted soils. Spheroids of organic material interpreted as excrement from enchytraeids dominated thin sections from the control and treated plots. Other observed excrement types were undifferentiated (fused) excrements formed from coalesced or “aged” excrements. The occurrence of the total excrements showed no faunal activity in plots polluted with 0.5%, 2.5% and 5% SP, indicating elimination of soil fauna by oil pollution. Results from point counting of excremental features indicated significant faunal activity with CD, PM and PW treatments, and in oil-polluted plots supplemented with organic wastes. The treatments with PM and PW were better than CD in stimulating oil degradation. Treatments also showed a reduction in total porosity with an increase in oil concentrations whereas no significant improvement was observed in oil-polluted soils amended with organic wastes. However, addition of the organic wastes to oil-polluted soils showed evidence of increased decomposition in the order PM > PW > CD. In conclusion, the substantial reduction in soil faunal activity as a result of oil treatment confirmed the deleterious effect of petroleum products on living organisms, but the addition of PM and PW were effective in ameliorating this negative impact.

Dry-cast concrete masonry products: properties and durabilityThis article is one of a selection of papers published in this Special Issue on Masonry.

Performance of dry-cast concrete masonry products (DCCMPs), which are becoming the product of choice for many applications, has yet to be assessed in a comprehensive manner. This study was undertaken to investigate the effects of mix design and manufacturing parameters on the mechanical and transport properties, as well as the freeze–thaw (F/T) durabilities, of DCCMPs. The variables studied were water to cement ratio, mixing time, vibration time, and curing regime. Freeze–thaw durability was assessed in accordance with the American Society for Testing and Materials (ASTM) standard C1262 by exposing specimens to four conditions: water, 3% NaCl, 4% CaCl2, and 4% MgCl2 solutions. Results revealed that 3% NaCl exposure yielded the most mass loss due to scaling, whereas 4% MgCl2 exposure exhibited the least. Increase in either water content, vibration time, mixing time, or use of moist curing led to improvement in the mechanical properties, refinement of large pores in the range of 40 to 400 μm, reduction of total porosity, and enhancement of F/T durability of capstones. Ionic sorptivity yielded a strong statistical correlation with mass loss due to F/T action in the presence of 3% NaCl and 4% CaCl2.

Effects of coarse fragment content on soil physical properties, soil erosion and potato production

Most potato (Solanum tuberosum L.) production in northeastern America is on till soils with an abundance of stones. Stone picking has removed many coarse fragments to a point that it might be detrimental to soil quality. This study was to assess the impacts of coarse fragment content (10–19 mm in diameter) on selected soil physical properties, field soil thermal and water regimes, runoff and soil loss and potato yield and tuber quality on a sandy loam soil in New Brunswick. The objectives were to evaluate both beneficial and adverse effects of coarse fragment content (0, 10, 20 and 30% by volume) on soil quality in relation to potato production over a 4-yr period. Soil bulk density increased significantly by incorporating 10 to 30% coarse fragments into the plow layer. Porosity and available soil water-holding capacity were reduced in response to this increase in bulk density. In spite of the reduction in total porosity, pore size greater than 148 µm diameter of the 30% coarse fragment treatment was significantly greater than the 0, 10 and 20% treatments during 2001, 1 yr after the treatments were applied. This increase in macropores may have been responsible for the significantly higher saturated hydraulic conductivity of the soil treated with 30% coarse fragments. The results from 2002 and 2003 show that these beneficial effects on soil physical properties were short lived in this study; however, this may not be the case under field conditions because experimental plot problems of relocation of coarse fragments beyond plot boundaries and/or dilution with incorporation of stone-free subsoil material is not an issue in the field. Volumetric water content at field capacity of −33.3 kPa matric potential declined from 20.9% for the control to 7.7% for the 30% coarse fragment treatment. Cumulative soil heat greater than 10°C of the 30% treatment showed significant increases of 11.2, 8.8, and 3.7% during the growing season of 2001, 2002, and 2003, respectively, as compared with the control. Although field soil water tension regimes revealed that soil water in different treatments was held at a somewhat similar energy status, field soil water content was reduced considerably with increasing amount of coarse fragments. No significant differences in runoff and soil loss were found between treatments, but average reductions in soil loss over the 3-yr period were 9, 36, and 47% lower than the control for the 10, 20, and 30% treatments, respectively. Although no significant difference in yield and tuber quality between treatments was found in 2001–2003, both total and marketable yield decreased with increasing time. The yield reduction over time may be directly attributed to the mono-culture of potatoes practiced during the course of this experiment. Key words: Soil temperature, soil moisture, conductivity, bulk density, tillage erosion, potato cropping

Compaction model for quartzose sandstones application to the Garn Formation, Haltenbanken, Mid-Norwegian Continental Shelf

The compaction of quartzose sandstones is described by a macroscopical visco–elasto–plastic model, derived from microscopical considerations. This model considers that the reduction of total porosity (the relative pore volume) is related to the changes in the relative cemented volume and the relative intergrain volume. Furthermore, we consider that the variations of these two petrophysical parameters result from two physical mechanisms, mechanical compaction and closed system chemical compaction.The model has been calibrated for the Middle Jurassic Garn Formation from the Haltenbanken area of the Mid-Norwegian Continental Shelf. Around 300 data points from 17 wells have been used in this study. The viscous parameters have been optimised against the present day data. With total porosity data the best fit is obtained for an activation energy between 14 and 16kJ/mole and a macroscopical viscosity at 15°C between 39 and 46GpaMa (1.21024–1.41024Pa.s). If quartz cement data are used, the best fit is obtained for an activation energy between 16 and 18kJ/mole and a macroscopical viscosity at 15°C between 47 and 56GpaMa (1.51024–17.1024Pa.s).The visco–elasto–plastic compaction model has been tested in the Haltenbanken area of Mid Norway, with the result that observed porosity trends and pore pressures can be modelled. Using multiple 2-D basin modelling simulations the results of this model and its implications for fluid flow and petroleum systems analysis can be seen. The compaction method has significant impact on the simulated fluid flow and petroleum migration pattern.

Efeito do pisoteio bovino em algumas propriedades físicas do solo de várzea

O objetivo do trabalho foi avaliar a influência do pisoteio de animais bovinos sobre propriedades físicas de um solo de várzea cultivado com consórcio de espécies forrageiras de inverno. Utilizaram-se azevém (Lolium multiflorum) + trevo branco (Trifolium repens) + cornichão (Lotus corniculatus), semeadas dia 05 de abril de 1997, em solo classificado como Planossolo, cuja área foi sistematizada em desnível de 0,06mm-1. O delineamento experimental foi o de blocos ao acaso com três tratamentos e seis repetições. Os tratamentos constaram das épocas de avaliação das características físicas do solo; T1 = antes da entrada dos animais, T2 = após a saída dos animais e T3 = seis meses após o término do pastejo. Cada piquete (Repetição) de 0,5ha constituiu-se numa parcela, adotando-se pastejo contínuo com terneiros de 8-10 meses de idade e carga inicial média de 480kg ha-1 de peso vivo, sendo que o resíduo de massa de forragem foi mantido ao redor de 1000kg/ha-1. O pisoteio animal ocasiona aumento da densidade do solo e redução da porosidade total. Nos primeiros cinco cm da superfície do solo, ocorre aumento da densidade do solo. Seis meses sem pisoteio não foram suficientes para que as raízes das plantas realizassem a descompactação do solo.

Cobertura do solo e degradação de pastagens em área de domínio de Chernossolos no sul da Bahia

O presente trabalho, realizado nos municípios de Itapé e Itaju do Colônia, os quais se encontram insertos na região econômica Litoral sul do estado da Bahia, teve por objetivo caracterizar um ambiente pastoril, dando ênfase a solos e sua cobertura natural, com a finalidade de mensurar e avaliar a degradação de pastagens. Essas áreas encontram-se em domínio de Chernossolos, em ambientes onde houve substituições de floresta nativa e cacau, cultivado em cabruca, por pastagens de capim Panicum maximum, cv. colonião e sempre-verde, cultivadas há vários anos em sistemas caracterizados como bem e mal manejados. Para isso, aplicou-se um método para análise da cobertura do solo, utilizando as unidades de amostragem de linhas e pontos em conjunto, monitorado pela caracterização química e física do solo. As amostras foram coletadas em trincheiras localizadas no topo, na meia-encosta e na baixada, em morros com conformações semelhantes. Verificou-se que a mudança de ambiente levou a alterações físicas e químicas do solo, tais como: diminuição nos valores de soma de bases, na capacidade de troca de cátions e, conseqüentemente, no grau de saturação por bases; diminuição nos teores de carbono orgânico total e aumento na densidade do solo e, em conseqüência, redução na quantidade total de poros, principalmente nas primeiras camadas do horizonte A, decorrente das exigências dos processos de conversão da floresta em pastagem. As amostragens realizadas por meio de linhas e pontos foram eficientes, uma vez que proporcionaram subsídios para a avaliação do nível de degradação, revelando que, ao longo dos anos, as pastagens mal conduzidas sofrem mudanças (sucessão de gramíneas, aumento na incidência de espécies espontâneas e de solo descoberto, dentre outras) que comprometem a sustentabilidade das pastagens da região.

Porosity In The Microstructure Of Blended Cements Containing Fly Ash

AbstractThe changes in porosity of OPC and an OPC-fly ash blended cement during hydration have been studied at water/solids ratios of 0.35, 0.47 and 0.59, cured for times of up to 1 year at 25°C. The porosity was measured indirectly by methanol exchange and methanol adsorption techniques and, directly, by quantitative image analysis using backscattered electron imaging in the scanning electron microscope. Measurements of porosity and of remaining anhydrous material by image analysis showed good correlation with indirect methods. Measurement of the diffusion of methanol and of the compressive strength were made in parallel with the determination of the porosity during hydration and attempts were made to relate the properties to the microstructure. For both binders the reduction of total porosity with increased reaction was small. The major change in pore structure was the subdivision of coarse pores by gel to form finer pores. Compressive strength and diffusion properties were dominated by the relative volume of coarse pores.

Porosity in the Microstructure of Blended Cements Containing Fly Ash

ABSTRACTThe changes in porosity of OPC and an OPC-fly ash blended cement during hydration have been studied at water/solids ratios of 0.35, 0.47 and 0.59, cured for times of up to 1 year at 25°C. The porosity was measured indirectly by methanol exchange and methanol adsorption techniques and, directly, by quantitative image analysis using backscattered electron imaging in the scanning electron microscope. Measurements of porosity and of remaining anhydrous material by image analysis showed good correlation with indirect methods. Measurement of the diffusion of methanol and of the compressive strength were made in parallel with the determination of the porosity during hydration and attempts were made to relate the properties to the microstructure. For both binders the reduction of total porosity with increased reaction was small. The major change in pore structure was the subdivision of coarse pores by gel to form finer pores. Compressive strength and diffusion properties were dominated by the relative volume of coarse pores.