Influencia de superplastificantes, ultra-som e revestimento com silicato de sodio nas propriedades de concreto

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

Concrete is the most widely used building material. Today, there is a strong interest in finding better ways of assessing the material properties of concretes which determine durabilily, since the degradation of concrete structures after prolonged exposure to environmental conditions should be minimized. In this work, some physicochemical properties of concrete are studied, with the aim of a better understanding of the factors envolved in the hydration reactions of cement. Mortar test specimens were obtained mixing 30% w/w ( Type I, ASTM C150-74 ) with 70% graded sand ( ASTM C33-74 ). Superplasticizer admixtures composed by 0.5 to 2.0% (v/v) sodium dodecylbenzene sulfonate (SDDS) and 0 to 4.0% (v/v) acetone were developed. Water reduction ranged from 8 to 28%, in the water/cement ratio. Sorptivity coefficients varied between 78 and 380 g.m.s (no admixture 744 g.m.s). Weight-loss after 300 hours imersion in 0.6M HCl varied betweem 2.8 and 4.8% ( no admixture: 6.5%). The best performance was observed with the 0.5% SDDS plus 4.0% acetone admixture; test specimen showed 52% increase in comperssive strenght, after 28 days. Results suggest that the SDDS molecules are strongly adsorbed onto the cement particles; acetone molecules increase this adsorption and are, themselves, preferentially adsorbed in the water/air surface, reducing air entrainment. Test specimen were coated with sodium silicate solutions containing 1.2, 0.8 or 0.6 M H2SO4 as precipitation agent. Water sorption ranged from 3.0 to 9.4% w/w ( uncoated: 9.3% ). Weight-loss after 300 hours inmersion in HCl varied from 0.5 to 5.7% (uncoated: 5.6%). The best performance was obtained using 1.2M H2SO4. Results suggest that an improovement in the coating process could yield an excellent protective agent. The fresh paste was sonicated at 25 and 40 kHz for 15, 60 and 120 minutes. The CO2 sortion of the 28 days-cured spacimens showed no difference with the non-sonicated specimens. The sorptivity coefficient ranged form 443 to 627 g.m.s (non-sonicated: 657 g.m.s); the best performance was observed in specimens sonicated at 25 kHz for 60 minutes. Results show that the effect of sonication is most pronounced in the exposed surface; there are evidences of changes in the hydration reactions.

ASSUNTO(S)

cimento portland concreto - analise

ACESSO AO ARTIGO

Documentos Relacionados