Influência de polímeros superabsorventes na retracção de argamassas

Hoje em dia, o desenvolvimento dos superplastificantes permite a produção de betões com menor razão água/cimento. Ao usar razões água/cimento mais baixas, os materiais científicos apresentam maior tendência para fissurar devido à retracção autogénea. Este trabalho apresenta um estudo sobre a utilização de polímeros superabsorventes (SAP) no controlo da retracção. O uso de SAPs em materiais comentícios atenua a retracção autogénea pois estes produtos permitem o fornecimento interno de água. Estes produtos podem também afectar outras propriedades, afectando as características mecânicas e a trabalhabilidade. Para análise do efeito dos SAP foram estudadas argamassas com várias concentrações deste produto, tendo como referência argamassas semelhantes sem SAP, determinando-se as retracções autogénea e total, a resistência à compressão e o módulo de elasticidade. Além de SAP, foi também utilizado um agregado leve, um outro tipo de introdutor de água, para comparação com os polímeros em estudo. /ABSTRACT: This work presents a study on the use of superabsorbent polymers (SAP) in the control of shrinkage. The use of SAPs in cementitious materials reduces the autogenous shrinkage because these products enable the internal supply of water. These materials can also affect other properties such as mechanical properties and workability. To analyze the effect of SAP, mortars containing various concentrations of this product were studied, in comparison with reference mortars without SAP. The tests performed were autogenous and total shrinkage, compressive strength and modulus of elasticity. Besides SAP, it was also used a lightweight aggregate, another type of internal supply of water, for comparison with the polymers under study.

A rapid staining-assisted wood sampling method for PCR-based detection of pine wood nematode Bursaphelenchus xylophilus in Pinus massoniana wood tissue

For reasons of unequal distribution of more than one nematode species in wood, and limited availability of wood samples required for the PCR-based method for detecting pinewood nematodes in wood tissue of Pinus massoniana, a rapid staining-assisted wood sampling method aiding PCR-based detection of the pine wood nematode Bursaphelenchus xylophilus (Bx) in small wood samples of P. massoniana was developed in this study. This comprised a series of new techniques: sampling, mass estimations of nematodes using staining techniques, and lowest limit Bx nematode mass determination for PCR detection. The procedure was undertaken on three adjoining 5-mg wood cross-sections, of 0.5 · 0.5 · 0.015 cm dimension, that were cut from a wood sample of 0.5 · 0.5 · 0.5 cm initially, then the larger wood sample was stained by acid fuchsin, from which two 5-mg wood cross-sections (that adjoined the three 5-mg wood cross-sections, mentioned above) were cut. Nematode-staining-spots (NSSs) in each of the two stained sections were counted under a microscope at 100· magnification. If there were eight or more NSSs present, the adjoining three sections were used for PCR assays. The B. xylophilus – specific amplicon of 403 bp (DQ855275) was generated by PCR assay from 100.00% of 5-mg wood cross-sections that contained more than eight Bx NSSs by the PCR assay. The entire sampling procedure took only 10 min indicating that it is suitable for the fast estimation of nematode numbers in the wood of P. massonina as the prelimary sample selections for other more expensive Bx-detection methods such as PCR assay.