International Concrete Abstracts Portal

Describes the effect of a superplasticizer and a viscosity-increasing admixture on the properties of high-strength lightweight aggregate concrete with a slump larger than 25 cm. Firstly, the compatibility between typical superplasticizers and the viscosity-increasing admixture was investigated. It has been reported that compatibility between sulfonated naphthalene formaldehyde condensate-typesuperplasticizer and a viscosity-increasing admixture was sometimes poor because of the gel production. It was found from experiments that maximum allowable dosages exist that do not cause the gel. Secondly, the effect of the superplasticizer and the viscosity-increasing agent on the properties of the concrete was investigated. The superplasticizer, containing a polymer called PVA, showed that larger dosages resulted in greater superplasticizing effect and constant slump flow. Furthermore, the viscosity-increasing admixture could prevent the concrete from harmful segregation. It was concluded that the degree of segregation depends on the dosages of super plasticizer and viscosity-increasing admixture. Furthermore, this research made it possible to obtain a high-strength (more than 41 Mpa) lightweight aggregate concrete with excellent flowability.

Atomic Energy of Canada Limited is undertaking a research and development program on cement-based grouts for possible use in sealing an underground nuclear fuel waste disposal vault. Silica fume and superplasticizer were added to a finely reground sulfate-resistant portland cement to produce a durable, low-permeability grout that would penetrate very fine fissures in granitic bedrock. The superplasticizer additive permits very low water-cement ratio grouts (w/c less than 0.6 by mass) that exhibit no segregation or bleed. The silica fume additive contributes to improved chemical stability and leach resistance of the grout. The developed grout has been injected into granitic rock at AECL's Underground Research Laboratory in Canada and at the NEA/OECD Stripa Facility in Sweden. No problems were encountered in the field trials in mixing, handling, or pumping of the grout. The injected grout produced only a very limited geochemical signature in the ground water and appears capable of penetrating microfissures in the granite with apertures of less than 20 æm.

The construction procedure of a nuclear containment concrete structure recently built required a highly workable concrete to facilitate placing around heavily congested steel embedments and reinforcements. Use of a superplasticizing admixture was considered essential. A test program was undertaken with several commercially available admixtures to study the properties of the fresh and hardened concrete made with low-heat cement (CSA: A5 Type 40). Under controlled conditions, four of these products met the construction requirements without adversely affecting the properties of the concrete.

Laboratory studies have been carried out to determine the leachability of the adsorbed superplasticizer (an Na-sulfonated naphthalene formaldehyde condensate) and its location within the structure of hardened cement tastes. The superplasticizer, labelled with 35 S, was incorporated in a reference cement-based grout (90 percent Type 50, 10 percent silica fume, 0.4 ó w/c ó 0.6). Static leaching tests were used to determine the release of labelled superplasticizer to solutions as a function of temperature, groundwater composition, and grout surface area to groundwater volume ratio. The quantity of 35 S in the leachate was determined using liquid scintillation counting. Electron-microautoradiography combined with scanning electron microscopy and energy dispersive x-ray spectroscopy were used to identify the cement phases containing the labelled superplasticizer. The results show that superplasticizer can be leached from grouts, but the cumulatively released quantities are very small (approximately 10(12 kg/mý). Most of the released superplasticizer appears to come from the capillary pore space of the hardened grout; however, some release may result from dissolution of the cement phases. Increasing temperature and/or grout surface area to groundwater volume ratio increases the release rate of superplasticizer. Analyses, using electron-microautoradiography and scanning electron microscopy, indicate that the majority of the adsorbed super plasticizer resides on the C-A-H phases and the calcium-rich phases of C-S-H in the cement.

In addition to a quickly obtained distinction between plasticizer and superplasticizer by means of a deflocculation test, it seems useful to complete this information by identifying their nature and chemical composition. Infrared spectrography, emission spectrometry, and wet chemical methods were applied to characterize various plasticizers. Methods employed were found to distinguish easily the various types of potential composition for such materials. They are therefore useful not only in establishing conformity of an admixture to previously submitted samples but also can discover the presence of potentially deleterious components.