International Concrete Abstracts Portal

Geopolymer is a specialized material resulting from the reaction of a source material that is rich in silica and alumina with alkaline solution. It is essentially portland cement free concrete. This material is being studied extensively and shows promise as a greener alternative to normal portland cement concrete. It has been found that geopolymer concrete has good engineering properties with a reduced carbon footprint resulting from the total replacement of normal portland cement. The research undertaken at Curtin University of Technology has included studies on geopolymer concrete mixture proportions, structural behavior, and durability. This paper presents the results on mixture proportions development to enhance workability and strength of geopolymer concrete. The influence of factors such as: curing temperature and régime, aggregate shape, strength, moisture content, preparation and grading, and the addition of superplasticizers, on workability and strength are presented.

From the 1930s to the 1970s a number of researchers in Russia, the U.S., and Canada worked on the development of a reliable pullout test. In Denmark, Kierkegaard-Hansen’s research first established pullout insert dimensions that resulted in a straight line relationship between the pullout force and compressive strength. This led to the development by Germann-Petersen of a portable tester suitable for site use. Subsequently, the procedure proved effective in assuring safe form removal times at early ages and in the acceleration of construction schedules. Experience worldwide over the last 30 years has established the usefulness of the test and it has been standardized in many countries.

In this study, the effects of high temperature on mechanical properties of high strength concrete were experimentally investigated. The effect of elevated temperatures ranging from 20 to 700 °C (68 to 1292 °F) on the material mechanical properties of normal-weight and lightweight aggregate high-strength concrete of 60 MPa grade was evaluated. Tests were conducted on Ø100 × 200 mm (3.94 × 7.87 in.) cylinder specimens. The specimens were tested under both stressed and unstressed conditions. The specimens were preloaded to 20 and 40% of their ultimate compressive strength at room temperature and subjected to temperatures ranging from 100 to 700 °C (212 to 1292 °F), and the compressive strength compared to that observed at 20 °C (68 °F).

The appearance of cracks and spalling in concrete columns in a new eight-story office building brought about concerns that the injection of the ducts in the columns was poor quality. The cracks were mainly present at one floor, and trial drillings into the ducts on columns with severe cracks disclosed the presence of water and loose gravel and aggregates. Opening a duct revealed that the duct was either partially empty, filled with compacted gravel, or fully grouted. It was decided to use the impact-echo (IE) method to investigate the columns and ducts. Each column contains four ducts with a 25 mm (1 in.) diameter reinforcing bar for distribution of the shear stress at the lower and upper 1.0 m (3 ft) to each floor. Testing was performed for each 0.1 m (4 in.) elevation in these areas. The criterion to approve the injection was that at least 0.7 m (2 ft) of the column at the floor or the ceiling was fully injected. After testing the columns on 3 floors, it was decided to investigate the ducts in the walls of the three stairwells of the building, as they were vital for transferring the stresses of the reinforcement down through the building. Verification of the IE-system by drilling cores showed that is possible to distinguish between empty ducts, fully injected ducts, and ducts with compacted gravel. More than 35,000 measurements were made. The examination of the ducts showed that approximately 63% of tests at the top and approximately 86% at the bottom of the columns and walls indicated full injection.

The presence of poor bonding at interfaces between, asphalt, membranes and concrete on bridge decks or between the original concrete and repair patches of tunnel linings often causes a faster deterioration of the different materials, resulting in for example corrosion of the reinforcement, which can lead to spalling of the concrete cover layer. Visual inspections often only disclose these problems at a late state in the deterioration process and repair or replacement of portions or the whole structure can be expensive. Regular inspections combining visual and NDT tools, such as the impulse-response technique and verification of the results by drilling out a few cores, can disclose problems at an early state and provides valuable information of the actual condition of the structure. The use of the impulse-response technique gives the user an indication of the mobility and stiffness of the structures and hence a tool to evaluate the presence of conditions such as poor bonding or delaminations in the structure. Large areas can be tested rapidly and data are valuable for planning future strategies for maintenance or repair of a structure. This paper presents some typical case histories with emphasis on the advantages and limitations of the impulse-response technique.