International Concrete Abstracts Portal

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.

Eight samples of sodium salts of naphthalenesulfonic acid-formaldehyde condensates with different molecular weight have been synthesized by stopping the polymerization process at different reaction times between zero (monomer) and 14 hr at 112 C using a molar H2SO4/naphthalene ratio of 1.07 and a molar HCHO/naphthalene ratio of 1.20. The longer the reaction time, the higher the molecular weight. The condensates have been analyzed by Gel Permeation Chromatography to determine the chemical composition and average molecular weight. The condensates have been used as superplasticizers (0.4 percent of dry product by weight of cement) for cement paste (water/cement ratio = 0.35) and the fluidifying effect has been determined by the mini slump test. It was found that the fluidifying effect increased by reducing the content of monomer and increasing the molecular weight of the condensate. To confirm that the fluidifying effect of the condensate substantially depends only on the content of the higher molecular weight fraction, two samples of the condensate, with different reaction times and then with a different condensation degree have been subjected to an ultrafiltration process. This technique allows removal of the monomer and the lower molecular weight fraction. The two samples of the condensate, which had different fluidifying effects before the ultrafiltration process, behaved similarly as superplasticizers after the ultrafiltration process.

Study was designed to assess the merits of polymer addition to superplasticized cement paste, mortar, and concrete. Three superplasticizers--a sulfonated melamine formaldehyde, a sulfonated naphthalene formaldehyde, and a commercial superplasticizer--were used in combination with experimental polymers. Polymer and superplasticizer dosages ranged from 0 to 15 percent and 0 to 0.3 percent, respectively. The effect of binary admixture systems (superplasticizer and polymer) on the physicomechanical properties of the cementitious systems was determined. Properties investigated included slump, slump retention, setting time, compressive strength, flexural strength, surface area, porosity, and density. Compatibility of the polymers with the superplasticizer was assessed with respect to the influence of the individual admixtures on the properties of the various systems. Synergistic effects were observed for one polymer, the results of which are discussed in detail.