995
4384.019
Not Given
Concrete Exposure Tests
Paper
Highway Research Board
1965
Post 1965
1-4 + charts
N
In 1962, the Thruway Authority instituted an exposure test of concrete slabs for the expressed purpose of finding materials that would give the maximum service in the maintenance repairs of structural concrete and to eliminate materials of marginal durability.Four factors were considered: (1) the use of wetting agents in the mix; (2) the choice of surface sealants; (3) the method of curing, and (4) the use of expanded shale aggregate.
Phase l, the winter of 1962-63, indicated that the use of wetting agents while increasing the compressive strength of the concrete and increasing the workability of the mix, produced an exposed surface that was extremely susceptible to the raves of de-icing chemicals. In Phase 2, we repeated the test slabs with similar results and, as a result, we discontinued the use of wetting agents in all further tests.
The second factor, the choice of sealants bore out what has become generally accepted. That the use of boiled linseed oil mixed with a petroleum solvent affords excellent production against spalling. Since we instituted a sealing program in 1963 as a routine maintenance practice, we discontinued further testing with this material.
The third factor, the method of curing definitely showed that the use of blankets had an adverse effect on the durability of the exposed surface. Air curing or rather the absence of any curing other than shading the specimens from direct sunlight, vastly improved the resistance of the surface to de-icing chemicals. It was obvious from the outset that, while this absence of curing was practical from a test standpoint, it was highly impractical from a field construction standpoint. Consequently, we compromised on the use of a membrane curing compound Hydrocide Resin X. The curing compound method has shown positive advantages over a curing method that places a burlap, paper or plastic surface in direct contact with the fresh concrete surface.
The fourth factor, the use of expanded shale aggregate, showed remarkable promise from the beginning.
In Phase 1, 1962-63, there were three slabs in which the fine aggregate was expanded shale and the coarse aggregate a hard local limestone.
In Phase 2, 1963-64, five more slabs using expanded shale were added to the test. Three were similar to the Phase 1 slabs in that the fine aggregate was 0″-1/4″ shale and the coarse aggregate was a hard local limestone, conforming to the N.Y.S.D.P.W. Specifications for #1 and #2 stone. The other two slabs were mixed using a 100% expanded shale aggregate of 0″-3/4″ gradation.
All five slabs were unsealed. At the conclusion of Phase 2, the three original and the five additional slabs evidenced no deterioration. The air content of these slabs ranged from a low of 3.5% to a high of 10.0%.
At the start of the second phase, Dow Corning Chemical Division asked us to try their product Dow 777. Consequently, we added two slabs of conventional aggregate utilizing Dow 777 as an additive. At the conclusion of Phase 2, both slabs were in excedllent condition.
As a result of what we had learned in Phases 1 and 2, we decided to concentrate on the two most promising leads; namely, expanded shale aggregate and Dow 777 Concrete Admixture. The admixture is, to quote the manufacturer, “a reactive polysiloxane designed for use in preparing concrete of superior durability.”
For Phase 3, we retained six of the 1962 slabs, three of which had expanded shale aggregate, twelve of the 1963 slabs, five of which had expanded shale wholly or partially as the aggregate and two of which had the Dow 777.
To these we added thirteen additional slabs, four of which contained Dow 777, five had expanded shale as the fine aggregate and four in which all aggregate was expanded shales.