A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C-S-H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q 2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.
A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C-S-H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q 2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.
Resumoste trabalho investiga o impacto da utilização de látex poliméricos em propriedades de pastas de cimento Portland branco no estado endurecido. Para tanto, foram utilizados dois látex com propriedades físico-químicas distintas: EVA (etileno de vinil acetato) em pó redispersível, e SAE (estireno acrílico) na forma de emulsão. As pastas foram preparadas com relação água/cimento constante de 0,40, e as quantidades de látex foram variadas, de 5% a 20% de constituintes ativos em relação à massa de cimento. Apesar de os látex poliméricos terem afetado negativamente a reação de hidratação do cimento de forma distinta, houve aumento na resistência mecânica e redução da absorção de água e da permeabilidade ao vapor, com maior teor látex/cimento.
Palavras
Santos, Hudson Chagas dos Análise de estruturas de concreto sob o efeito do tempo: uma abordagem consistente com a consideração da viscoelasticidade, da plasticidade, da fissuração, da protensão e de etapas construtivas / H.C. dos Santos.-São Paulo, 2006. 132p. Tese (Doutorado)
The use of waste glass powder (WGP) as a supplementary cementitious material (SCM) rich in pozzolan as a partial replacement for cement has been a viable alternative, from the environmental and economic point of view, to solve problems caused by the high consumption of cement worldwide. Therefore, the objective of this study was to evaluate the effects of the use of WGP, when used as a partial cement substitute, in some properties of cementitious composites (pastes, mortars and concretes), in the fresh and hardened state. Through a systematic literature review, 23 experimental research articles obtained from the world-renowned Science Direct database were analyzed. The results obtained from this review indicate improvements in some properties of cementitious composites with WGP, such as increased compressive strength at advanced ages, increased thermal neutron shielding capacity, reduced penetration of sulfate and chloride ions, mitigation of alkali-silica reaction, reduced thermal conductivity, improved mechanical and chemical properties, including the formation of a new crystalline phase (devitrite) when exposed to high temperatures, reductions in air entrapment, water absorption and porosity. Regarding workability, there was no consensus, however, regardless of the substitution content, all composites were within the slump limits. Therefore, it can be concluded that the use of WGP in cementitious materials produces beneficial effects on some properties of cementitious composites.
Arquitetura em arcos e soluções de recuperação estrutural: estudo de caso da Igreja Matriz de Nossa Senhora do Amparo, Teresina-PI Arch architecture and structural recovery solutions: a case studyof the Mother Church of Nossa Senhora do
Nos grandes centros urbanos, a constante impermeabilização das vias intensifica alagamentos e enchentes, gerando inúmeros transtornos à população. O uso do concreto permeável como mecanismo de drenagem de águas pluviais e residuárias tem sido uma solução parcial para esse tipo de problema de drenagem, inclusive com a adição em sua composição de materiais com propriedades adsorventes que visem a melhoria de parâmetros físico-químicos e biológicos da água. Portanto, este artigo tem como objetivo geral trazer importantes resultados de diversos estudos utilizando concreto permeável com adições minerais e mostrar os benefícios nas propriedades mecânicas e adsorventes desse tipo de concreto, com ênfase na utilização do biocarvão. Para isso, optou-se como metodologia, fazer uma breve revisão da literatura, no qual foram analisadas pesquisas concluídas disponíveis em base de dados online como Scopus, Science Direct a partir do ano de 2015 utilizando como descritores em inglês: “Concrete” AND “Biochar”, “Concrete porous” AND “Biochar”, “Pervious concrete” AND “Biochar”, “Treatment of water” AND “Concrete porous”, “Cementitious materials” AND “Biochar”. Foram selecionadas 51 referências sendo assim especificados: 48 artigos científicos, 1 norma e 2 capítulos de livros. Constatou-se que a adição de minerais adsorventes e biocarvão no concreto podem promover melhoria de parâmetros de qualidade da água como diminuição de turbidez, nitrogênio totais (NT), Fósforo Totais (PT), DQO, DBO, entre outros, e promoverem, em alguns casos, ganho de resistência mecânica dos concretos produzidos.
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