International Concrete Abstracts Portal

The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources Canada, Ottawa, has played a significant role in Canada for over 40 years in the broad area of concrete technology. In recent years, CANMET has become increasingly involved in research and development dealing with supplementary cementing materials, high-performance normal-weight and lightweight concretes, and alkali-aggregate reactions. In May 2004, CANMET, in association with the American Concrete Institute and several other organizations in the United States, sponsored the Seventh CANMET/ACI International Conference on Recent Advances in Concrete Technology in Las Vegas, U.S.A. Seventeen refereed papers from more than 10 countries were presented and distributed at the conference. The proceedings consisting of refereed papers were published as ACI SP-222. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP222

Lignosulphonate is a widely used plasticizing admixture in concrete. It is well documented that different qualities of this material give different performance in concrete. Depending on what kind of concrete that is needed, workability can be controlled by adding different amounts or qualities of the lignosulphonate. This investigation compares the adsorption of lignosulphonate on three different portland cements, to the rheological properties of cement pastes made from the same cements. The adsorption isotherms were calculated from depletion experiments. A rheometer with bob-cup geometry was used to measure the rheological properties of the cement pastes. The plasticizing effect of lignosulphonates in cement paste slurries was confirmed. Recent advances have given a novel lignosulphonate with superplasticizer performance. This investigation demonstrates these improved properties achieved by this novel lignosulphonate by determining the differences in adsorption of the different lignosulphonates, on cements with different chemical characteristics.

This paper presents the effect of mixture composition on the compressive strength of fly ash-based geopolymer concrete. Test results show that water-to-sodium oxide (H2O-to-Na2O) molar ratio and the water-to-geopolymer solids ratio by mass influence the compressive strength of fly ash-based geopolymer concrete. The compressive strength decreases when these ratios increase. However, the sodium oxide-to-silicon oxide (Na2O-to-SiO2) molar ratio of the geopolymer mixture does not have any significant effect on the compressive strength within the range of 0.095 and of 0.120 of this ratio.

A long-term research study on anti-corrosion products for reinforced concrete exposed to aggressive environmental conditions was initiated in 1990. The performance of products was evaluated through accelerated laboratory testing and natural site expo-sure conditions as tidal zone, above ground and below ground. An exposure site on the Dubai creek shore is designated for long term performance testing at different ages ex-tending up to ten years. A series of physical and electrochemical testing were performed in three phases. The prime objective of the first phase was to assess the performance of the various products, and to assess the practical value of different electrochemical test methods. The focus of the second phase testing shifted towards a more comprehensive evaluation of the test methods. The interim results have been presented at different international conferences. The focus of third phase, which was performed in early 2000, was to observe the actual extent of corrosion sustained by the rebar. This paper presents the final data to substantiate conclusions relating to ingress of chlorides for the various exposure conditions (threshold values), provides recommendations for corrosion monitoring for new structures and test methods for evaluating products and future research requirements.

Ettringite observed in macroscopic paste cracks during DEF is often held responsible for concrete deterioration. However, some authors have raised the hypothesis of an homogeneous paste expansion resulting from ettringite crystallisation in the C-S-H porosity, which does not attribute any mechanical effects to the subsequent formation of ettringite crystals in the voids. Thus the role of ettringite is still controversial. In this paper, we are tempting to link the two previous hypotheses in a more global mechanism: During heat treatment, thermal decomposition of ettringite can occur, whereas higher amount of sulphate and aluminate are trapped into C-S-H porosity. Then, at ambient temperature, ettringite forms in the porosity corresponding to the network of C-S-H layers. If the volume of ettringite reaches the limit of C-S-H porosity, the following ettringite crystallisation induces an homogeneous expansion of the paste. This expansion can generate peripheral cracks around aggregates. Then, the local shrinkage around voids resulting from the dissolution of the small ettringite crystals incorporated in C-S-H layers and the following precipitation of ettringite massive crystals in the cracks due to Ostwald rippening, outbreaks radial cracks. When the material is weaken by a multidirectional crack network, the pressure exerted by massive ettringite crystallisation can propagate existing cracks by strain localisation at the crack's tip, even if the crystallisation pressure is small in these conditions.