ACI Global Home Middle East Region Portal Western Europe Region Portal
Email Address is required Invalid Email Address
In today’s market, it is imperative to be knowledgeable and have an edge over the competition. ACI members have it…they are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them.
Read more about membership
Learn More
Become an ACI Member
Topics In Concrete
Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 90 Abstracts search results
Document:
SP132-39
Date:
May 1, 1992
Author(s):
J. Philip and J. R. Clifton
Publication:
Symposium Papers
Volume:
132
Abstract:
Engineered enchancement of or engineered alternatives to shallow land disposal of low-level radioactive (LLW) is likely to be the disposal technique adopted by a majority of states in the U.S. Such disposal techniques involve extensive use of concrete as an engineered barrier to prevent the escape of radionuclides into the environment. The LLW will be contained in concrete vaults or bunkers buried underground or covered with earth. U.S. Regulation 10 CFR 61 establishes the regulatory responsibilities for licensing LLW disposal sites. Implicit in the regulations is the need for the concrete of the LLW disposal system to have a service life of 500 years. Discusses the regulatory responsibilities governing LLW disposal. It also discusses results of a research project at the National Institute of Standards and Technology for the U.S. Nuclear Regulatory Commission to predict the service life of underground concrete for LLW applications. Assuming that disposal will be above the water table, the major degradation mechanisms affecting the concrete would be those due to sulfate attack, chloride ions, alkali-aggregate reaction, and leaching. Mathematical modeling of the degradation mechanisms and the validation of those models with accelerated laboratory tests suggests that service lives of 500 years for concrete structures can be reliably achieved.
DOI:
10.14359/1323
SP132-47
H. Justness, E. J. Sellevold and G. Lundevall.
Cement pastes of interest for high-strength concrete technology were investigated by high-resolution solid state magic angle spinning (MAS) Si-nuclear magnetic resonance (NMR) in combination with thermal analysis (DTA/TG). NMR reveals the degree of hydration for C3S/C2S in cement, pozzolanic activity of condensed silica fume, and average chain length of the silicate anions in the CSH-gel. A combination of NMR and DTA/TC data gives the empirical formula of the CSH-gel. The binders investigated were made from blended portland cement containing 0, 8, and 16 percent cement replacement with condensed silica fume and water-binder ratios of 0.20, 0.30, and 0.40. The specimens were allowed to cure in sealed conditions for 1, 3, 7, 28, 126, and 442 days. The results confirmed that condensed silica fume is a very reactive pozzolan. The conversion rate of condensed silica fume to hydration products after 3 days of curing was, in fact, higher than for the neat cement at the same age. After 3 days of curing, condensed silica fume reduced the degree of hydration of the cement in the blended cement pastes when compared with pastes without it. The effect was enhanced at later ages when the cement hydration process stopped while the pozzolanic reaction continued to near completion. In regard to the composition of the CSH-gel, it was found that the average chain length for the linear polysilicate anions increased with decreasing w(c + s) and, in particular, with increasing dosages of condensed silica fume. Furthermore, the c/s of the gel decreased considerably with increasing dosages of condensed silica fume. The mechanism of the pozzolanic reaction of condensed silica fume is discussed.
10.14359/2304
SP132-40
J. Ambroise, S. Martin-Calle, and J. Pera
After calcination at 650 to 850 C, kaolinitic clays show an interesting pozzolanic property. Thermal activation leads to metakaolin, an amorphous phase which is very reactive. In this study, different clays were tested with various granular sizes and calcination parameters. The pozzolanic properties were investigated using metakaolin-lime mixtures by the evaluation of both the mechanical strength and combined lime. The mineralogical composition, particle size distribution, and degree of amorphousness were the main factors affecting the pozzolanic activity of calcined clays. Influence of the pozzolanic activity on the mechanical and durability properties of concrete was established from test results on blended portland-metakaolin cements.
10.14359/2133
SP132-42
T. Marwan J. Pera, and J. Ambroise
When heated at 800 C for 5 hr, Indonesian laterites showed good pozzolanic activity. The kaolin content of the material is the main cause of pozzolanicity, as indicated by the lime reactivity. Blended portland cements containing 20, 30, 40, and 50 percent of calcined laterite admixture were studied. Concretes were made with such cements and placed in aggressive solutions: seawater, acetic acid, and sulfuric acid. The best results were obtained with a cement containing 30 percent of calcined laterite admixture.
10.14359/2144
SP132-43
R. Breitenbucher, R. Springenschmid, and H. W. Dorner
In tunnels built according to the New Austrian Tunnelling Method, the shotcrete shell is often in contact with ground water. Depending on the amount and type of water, chemical compounds in the shotcrete are dissolved and transported into the drainage pipes and the main outfall. Due to precipitation of the dissolved compounds, the maintenance of the drainage systems is very expensive. Furthermore, the main outfall is loaded with water of a high pH-value. It was found that as well as Ca(OH)2, the alkalies in the shotcrete are responsible for the degree of leaching. Therefore, the accelerators needed for such shotcretes, which are based mostly on alkalies, have to be reduced as much as possible. This can be done sufficiently if silica fume is used in connection with slag cement to make the shotcrete sticky enough, so that it adheres to the rocks.
10.14359/2155
Results Per Page 5 10 15 20 25 50 100
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Edit Module Settings to define Page Content Reviewer