Effects of superplasticiser on rheology and cohesiveness of CSF cement paste

Superplasticiser (SP) is now an indispensable ingredient for the production of concrete. However, its proper use is a great concern because its over-dosage could lead to drastic reduction in the cohesiveness of concrete. Furthermore, experience has indicated that the SP demand, saturation dosage and dosage causing segregation are highly dependent on the powder content and therefore the effects of SP are not simple functions of dosage. This study aims to evaluate the effects of SP dosage on the fresh properties of cement paste containing condensed silica fume (CSF). A number of cement paste samples with different SP dosages and CSF contents were tested. The results showed that the addition of SP would improve the packing density, flowability and rheology but impair the cohesiveness of cement paste. It would also render the cement paste shear thickening. To cater for the effects of powder fineness, it is proposed that the SP dosage should be measured in terms of the quantity of SP per surface area of the powder content. © 2012 Thomas Telford Ltd.published_or_final_versio

Improving particle size distribution in cement paste by blending with superfine cement

The rheological and mechanical performance of cement paste is closely related to its packing density, which may be optimized by improving the particle size distribution in the paste mix. In this study, the authors propose modifications to the existing mathematical equations of particle size distribution. The new equation of optimal particle size distribution so formulated is verified experimentally. A series of cement paste having different water/cementitious materials (W/CM) ratios were produced by blending ordinary Portland cement (OPC) with varying contents of superfine cement (SFC). The particle size distributions of the blended paste mixes were compared with the proposed equation. The packing density of paste mixes was measured using the wet packing test method, and the flowability, rheological properties, and compressive strength of the paste mixes were tested. It is found that the particle size distribution in cement paste can be improved by blending with SFC, which can lead to enhancement in packing density, flowability, rheology and strength. The authors opine that the proposed equation of particle size distribution may be applied for mix design optimization of cementitious paste, including cementitious grout and the paste phase in mortar and concrete.published_or_final_versio

Packing density improvement through addition of limestone fines, superfine cement and condensed silica fume

Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.published_or_final_versio

Effects of Fly Ash Microsphere on Flowability and Cohesiveness of Cement Paste

Paper No. M214This study evaluates the effects of fly ash microsphere (FAM) on the flowability and cohesiveness performance of cement paste. FAM is a superfine fly ash captured from the coal-fired power stations. It has a mean particle size of around 2 mm and is of spherical shape. An experimental program comprising a total of 38 cement paste mixes was launched and the flowability and cohesiveness performance of the mixes were measured. Results showed that addition of FAM up to 40% by volume could improve the flowability but decrease the cohesiveness at the same water to cementitious materials (W/CM) ratio. In general, the cohesiveness of cement paste would decrease with increasing flowability.published_or_final_versio

Use of Limestone Fines to Reduce Permeability of Concrete for Durability Improvement

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Application of whole exome sequencing in metachronous lung cancers evaluation

Poster Abstracts: no. 69Conference Theme: Cancer GenomicsMultiplicity and metachronous tumours are recurrent management problems. Morphological resemblance, in-situ carcinoma, cancer driver mutations, etc. have been used to distinguish intrapulmonary metastasis and metachronous primary lung cancers but these criteria are often insufficient. Next generation sequencing promises to advance personalized cancer management but finding a practicable approach remains a problem. We explored the utility of whole exome sequencing for cancer nature determination in a 74 year-old female non-smoker with 2 sequential lung cancers of unknown relation. Initially, she had an EGFR-L858R adenocarcinoma (Tumour-A) treated by excision and adjuvant gefitinib for metastatic pleural tumours. Two years later while ...postprin

Vitamin and mineral supplements in pregnancy and the risk of childhood acute lymphoblastic leukaemia: a case-control study

<p>Abstract</p> <p>Background</p> <p>An earlier case-control study from Western Australia reported a protective effect of maternal folic acid supplementation during pregnancy on the risk of childhood acute lymphoblastic leukaemia (ALL). The present study tested that association.</p> <p>Methods</p> <p>A national case-control study was conducted in New Zealand. The mothers of 97 children with ALL and of 303 controls were asked about vitamin and mineral supplements taken during pregnancy.</p> <p>Results</p> <p>There was no association between reported folate intake during pregnancy and childhood ALL (adjusted odds ratio (OR) 1.1, 95% confidence interval (CI) 0.5–2.7). Combining our results with the study from Western Australia and another study from Québec in a meta-analysis gave a summary OR of 0.9 (95% CI 0.8–1.1).</p> <p>Conclusion</p> <p>Our own study, of similar size to the Australian study, does not support the hypothesis of a protective effect of folate on childhood ALL. Neither do the findings of the meta-analysis.</p