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Showing 1-5 of 63 Abstracts search results

Document: 

SP79-53

Date: 

May 1, 1983

Author(s):

Jiro Murata, Michio Kawasaki, Takeshi Sakai, and Tadashi Kawai

Publication:

Symposium Papers

Volume:

79

Abstract:

The generally high resistance to freezing and thawing of concrete using ground blast-furnace slag as sand is noted, and from the standpoint of effective utilization of waste materials, development of positive uses for blast-furnace slag sand is studied.

DOI:

10.14359/6736


Document: 

SP79-46

Date: 

May 1, 1983

Author(s):

M. Regourd, B. Mortureux, and H. Hornain

Publication:

Symposium Papers

Volume:

79

Abstract:

At early ages, blended cement mortars with 30 % hydraulic slags or active pozzolans have lower mechanical strengths than mortars incorporating 100 % Portland cement. The action of 5 % condensed silica fume replacement for slag or pozzolan or material considered as inert has been studied from 7 days to 3 months by measuring the mechanical strengths of mortars made according to IS0 test method and by observing the microstructure of fractured samples. This action of the condensed silica fume is a function of the nature of the additive. With hydraulic slags, there is a competition between slag and silica fume for the available lime. With slightly or slowly reactive pozzolans (volcanic rock, fly ash) mechanical strengths and microporosity of mortars show improve-ment at 28 days. With inert materials (crystalline slag or quartz), the improvement is more marked. This is due to the formation of dense C-S-H, strong cement paste-aggregate bond and 20 % increase in mechanical strengths.

DOI:

10.14359/6729


Document: 

SP79-11

Date: 

May 1, 1983

Author(s):

U. Costa and F. Massazza

Publication:

Symposium Papers

Volume:

79

Abstract:

Properties of pozzolanic cements made by mixing 30% of fly ashes with 70 wt. % of portland cements are studied as a function of fineness. The fineness of the two components ranged between 3260-6940 and 3520-8190 cm2/g (Blaine) respectively. The reaction between fly ash and lime released by clinker silicates becomes apparent after seven days. Combined calcium hydroxide increases with fineness. Replacing 30% clinker + gypsum by fly ash causes a decrease in 1 day-mortar strengths by about 50%. This decrease is recovered in the following days as from 14-28 days the strength of bl ended cements exceeds 70% of that of control cements. Early mechanical strengths of mortars are affected more by the fineness of portland cement than that of fly ash. The opposite occurs for strengths at long ages. Till 7 days fly ash reduces the heat of hydration considerably less than strengths. Yield value and plastic viscosity of cement paste increase when fly ash is ground. The stren gth and h eat of hydration results suggestthatpozzolanic reaction begins before what supposed on the basis of calcium hydroxide conten t of the pastes.

DOI:

10.14359/6694


Document: 

SP79-38

Date: 

May 1, 1983

Author(s):

0ystein Vennesland and Odd E. Gjorv

Publication:

Symposium Papers

Volume:

79

Abstract:

The good ability of concrete to protect embedded steel against corrosion is mainly due to the high alkalinity of the pore water of the concrete, which provides a passive, noncorroding state of the embedded steel If this passivity of the steel is broken - either by carbonation or by the presence of chloride ions the corrosion of the steel will mainly be controlled by the electrical resistivity of the concrete and the rate of oxygen transport through the concrete to the steel. The present paper describes a study on how additions of up to 20% condensed silica fume by weight of cement affect the rate of carbonation, electrical resistivity and rate of oxygen transport through water-saturated concrete. It was found that the effect of silica on the parameters studied varied within wide limits, The rate of oxygen transport was only slightly affected while the rate of carbonation was somwhat reduced. The most pronounced effect of silica was found on the electrical resistivity which is increased by up to 190-1600% for cement contents varying from 100 to 400 kg/m3, respectively.

DOI:

10.14359/6721


Document: 

SP79-22

Date: 

May 1, 1983

Author(s):

R.F. Feldman

Publication:

Symposium Papers

Volume:

79

Abstract:

Normal portland cement mixed separately with two types of fly-ash and ground quartz to produce blends containing 35 per cent additive and a mix containing 70 per cent slag were cured in water at 21, 35 and 55'C at a w/c = 0.45. After 2, 7, 14, 28, 90, 180, 365 and 550 days, Ca(OH)2 content, pore size distribution, compressive strength, Young's modulus and microhardness of the products were determined. Density and porosity were measured by mercury intrusion, helium pycnometry and methanol saturation. Mortars were also prepared using these blends. After curing for 15 or 240 days they were exposed to a salt solution containing 27.5% CaC12, 3.9% MgC12, 1.8% NaCl and 0.1% NaHCO3. The porosities of the hydrated blends were higher when measured by mercury intrusion and had a higher percentage of fine pores. Densities of the products calculated from these pore measurements gave more realistic values. Higher temperatures increased the early rate of reaction of the cement, then retarded it, but the acceleration period was extended for the cement blends. Factors responsible for durability were found to be pore volume above 88 nm diam and Ca(OH)2 content.

DOI:

10.14359/6705


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