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International Concrete Abstracts Portal

Showing 1-10 of 46 Abstracts search results

Document: 

SP149-45

Date: 

October 1, 1994

Author(s):

J. J. Schemmel, , M. L. Leming, and M. R. Hansen

Publication:

Special Publication

Volume:

149

Abstract:

A 4-year study, conducted by a consortium of three universities, on the use of high-performance concrete in highway applications was recently completed. A major goal of this research project was to determine if high-performance concrete mixes could be successfully produced in the field. In addition, an evaluation was to be made of the long-term performance of this concrete under field service conditions. Field installations were constructed in five states for this purpose. Paper provides potential users of high-performance concrete with general recommendations and guidelines for production and placement.

10.14359/4294


Document: 

SP149-44

Date: 

October 1, 1994

Author(s):

G. C. Hoff

Publication:

Special Publication

Volume:

149

Abstract:

The use of high-strength lightweight concrete (HSLWC) in offshore oil and gas platforms is becoming more common. The constant wave action on these structures imposes continual fatigue loading on the concrete. Paper reviews previous research on both compressive and flexural fatigue behavior of HSLWC. The fatigue behavior of HSLWC is comparable or somewhat better than high-strength normal-density concrete (HSNDC) tested under the same conditions. The cyclic strain behavior of HSLWC is significantly different than for HSNDC and there is little change in strain behavior with increasing cycles of load until failure occurs. The fatigue life is reduced when the concrete is tested in submerged conditions. There is no significant difference between the S-N curves for reinforced and nonreinforced concrete. The mechanism that causes HSLWC to have comparable or better performance than HSNDC is attributed to the improved microstructure of the matrix-aggregate interface. This improvement reduces microcracking that typically leads to fatigue damage. The effect of crack blocking by sea salt depositions is discussed.

10.14359/4286


Document: 

SP149-43

Date: 

October 1, 1994

Author(s):

C. T. Thornton

Publication:

Special Publication

Volume:

149

Abstract:

The twin 450-m Petronas Towers under construction in Kuala Lumpur City Centre, Malaysia, are discussed. These world's tallest buildings use concrete columns, ring beams and a core of 40- to 80-MPa cube strength concrete, and steel long-span floor beams. Benefits of high-strength concrete are discussed, including occupant comfort achieved using mass-to-length building period and high inherent damping to reduce building response, high lateral stiffness, simple monolithic cast in situ connections, reasonable member sizes, local labor use, and light erection equipment. Special design features include deep barrette foundations acting in friction, temperature control measures for a massive mat pour, treatments at stepped and sloping columns, and use of haunched beams to accommodate mechanical ducts. The construction approach to creep and shrinkage is also discussed.

10.14359/4256


Document: 

SP149-42

Date: 

October 1, 1994

Author(s):

W. Jiang and D. M. Roy

Publication:

Special Publication

Volume:

149

Abstract:

The main topic focuses on a materials science approach to evaluating three major strengthening mechanisms of high-performance concretes: reduced porosity by low water-cement ratio, absence of macro-defects, and synthetic composition mechanism. The substantially improved cement matrix materials can be obtained by deliberately using one or more of the preceding mechanisms. The preliminary experiments were carried out by two computer coupled techniques, one utilizing an electromechanical linear variable differential transformer (LVDT), while the toughening experimental technique was based on determining the J-integral to obtain K 1 c and G 1 c in an indirect way suing small-size specimens. An acoustic emission system was also used. At different concrete maturity stages, the acoustic emission signal generated from the microstructure is transformed due to wave propagation and the transducer response. The data are analyzed numerically. The results obtained through this study are expected to contribute to the establishment of a new strengthening concept of high-performance concrete. The objective of this paper is to sketch a new approach to a group of strengthening phenomena that are as important from a theoretical viewpoint as they are useful for technology.

10.14359/4184


Document: 

SP149-41

Date: 

October 1, 1994

Author(s):

B. Fournier and V. M. Malhotra

Publication:

Special Publication

Volume:

149

Abstract:

Two Canadian aggregates, a reactive siliceous limestone and nonreactive crushed granite, were evaluated for their potential alkali reactivity (AAR) in high-performance concrete. The concretes were proportioned to have high strength and cement content greater than 400 kg/m 3. Concrete mixes were made using a silica fume blended cement and a cementitious system in which 25 percent of a CSA Type 20 low-alkali cement was replaced by ASTM Class F fly ash. Also, control mixes were made with a CSA Type 10 high-alkali cement. The susceptibility to AAR of these concrete mixes was evaluated by casting concrete prisms and subjecting them to various accelerated storage conditions in the laboratory. For comparison purposes, mortar bars were also made, and tested according to the ASTM P 214 (1990) accelerated mortar bar test procedure. The AAR concrete prism tests performed in this study have shown that none of the concrete prisms made with silica fume blended cement and low-alkali cement incorporating fly ash showed significant expansion after 18 to 24 months of testing either in 1N NaOH or in exposure conditions of 38 C and relative humidity greater than 95 percent. The accelerated mortar bar test results, however, suggest that long-term testing may be needed to evaluate the effectiveness of blended cements in reducing expansion due to AAR, especially for highly reactive aggregates.

10.14359/4118


Document: 

SP149-40

Date: 

October 1, 1994

Author(s):

Y. Sitsutaka, K. Kamimura, and S. Nakamura

Publication:

Special Publication

Volume:

149

Abstract:

The influence of aggregate properties on the tension-softening behavior of high-strength concrete was studied. A new method to determine the tension-softening curve of concrete is proposed, based on the polylinear approximation analysis. The prediction method for the load-displacement relationships of concrete with cracks is developed by means of the fictitious crack model concept with the K-superposition method and constitutive law with the polylinear tension-softening curve. In this method, nonlinear crack equations were solved by the iteration program for evaluating softening inclinations. The polylinear approximation method for calculating the complete tension-softening curve from the actual load-displacement curve was established by using nonlinear crack equation analysis. Tension-softening curves of concrete with various aggregates and matrix strengths were measured, and their characteristics were discussed.

10.14359/4182


Document: 

SP149-39

Date: 

October 1, 1994

Author(s):

S. Nakamura, Y. Kitsutaka, and K. Kamimura

Publication:

Special Publication

Volume:

149

Abstract:

The interaction between aggregates and mortar matrix is an important factor for improving the strength and toughness of high-strength concrete. Experimental investigations were carried out on the influence of aggregate properties on fracture energy G F of high-strength concrete. The influence of mortar matrix strength and volume fraction of coarse aggregate on fracture energy has been tested by three-point bending in Mode I loading. The interaction between aggregates and mortar matrix was estimated by the energy balance concept on the fracture energy of aggregate inclusion G Fi and that of mortar matrix G Fm. According to the test results, G F is strongly influenced by strength properties and volume fraction of aggregates. It was clear that the improvement of toughness of high-strength concrete is obtained by using high-strength aggregate and by designing a large volume fraction of coarse aggregate.

10.14359/4180


Document: 

SP149-38

Date: 

October 1, 1994

Author(s):

C. Yan and S. Mindness

Publication:

Special Publication

Volume:

149

Abstract:

Bond reinforcing bars and concrete under impact loading were studied for both plain and steel fiber reinforced concretes. Experiments consisted of both pullout tests and push-in tests. The design compressive strengths of the concrete were 40 MPa (normal strength) and 75 MPa (high strength) at 28 days. The impact loading induced bond stress rates ranging from 0.5 x 10 -4 to 0.5 x 10 -2 MPa/sec. The bond under stress rates ranging from 0.5 x 10 -8 to 0.5 x 10 -4 MPa/sec was also studied for comparison. Each reinforcing bar was instrumented with five pairs of strain gages to monitor the actual strains during the bond-slip process. All test data were collected by a high-speed data acquisition system at a sampling rate of 200 sec. Stress distributions in both the steel and concrete, bond stresses and slips, bond stress-slip relationships, fracture energy in bond failure, and internal crack development were investigated. It was found that compressive strengths increased the bond-resistance capacity and fracture energy in bond failure, and therefore had a great influence on bond stress-versus-slip relationship. This effect was increased by high loading rates and steel fiber additions, especially for the push-in loading mode.

10.14359/4178


Document: 

SP149-37

Date: 

October 1, 1994

Author(s):

T. D. Lin

Publication:

Special Publication

Volume:

149

Abstract:

Cement particles generally consist of micropores measuring 5 to several hundred. The micropores are too small to permit permeation of water due to water surface tension, but large enough to accommodate diffusion of steam under elevated pressure. The size of a water molecule has been scientifically determined. When dry cement particles are in contact with steam, heat immediately transfers from steam to cement, and part of the steam is forced into inner regions of the cement particles via the micropores. As a result, cement particles gain activation energy, and at the same time steam partially condenses due to energy dissipation to form moisture coating on the surfaces of cement particles as well as the interior surfaces of the micropores. Both the activation energy and condensation of steam enhance a rapid and complete hydration. Test results show that concrete made with the dry-mix/steam-injection procedure developed high CSH/CH ratios in paste and a high strength of 700 kgf/cm 2 (10,000 psi), approximately 2.5 times that of companion concrete made with the wet-mix procedure, in less than 1 day. Another test series demonstrated a 50 percent reduction of cement requirement in comparison with the wet-mixed concrete with an equivalent strength of 560 to 630 kgf/cm 2 (8000 to 9000 psi).

10.14359/4117


Document: 

SP149-36

Date: 

October 1, 1994

Author(s):

C. T. Tam, Y. H. Loo, and K. F. Choong

Publication:

Special Publication

Volume:

149

Abstract:

The control of differential thermal stress or strain due to heat of hydration in a thick concrete section can be a requirement for a high-performance concrete. An investigation was carried out to study the use of ground granulated blast furnace slag (GGBFS) as partial replacement of cement to reduce the adiabatic temperature rise of concrete. By testing concrete mixes instead of cement pastes, this study includes the effects of not only the cement but also the presence of aggregates in their proportions and directly relates the mix to the job. A computer-controlled cell is designed to measure the adiabatic temperature rise in concrete with initial concrete temperature at 20, 30, or 40 C. Slag replacement up to 70 percent by mass of total cementitious binder content was studied. Other parameters studied include water-binder ratio ranging from 0.40 to 0.60, fineness from 300 to 400 kg/m 2, and binder content from 250 to 350 kg/m 3 of concrete. The results of the adiabatic temperature rise in concrete show that an increase in slag replacement reduces the temperature rise. The effect of higher fineness or higher total cementitious binder content leads to higher temperature rise. However, the influence of placing temperature on the temperature rise indicates a lower rise at higher placing temperature. It is also noted that at higher placing temperature, slag replacement greater than 55 percent by mass tends to reduce temperature rise to a greater extent than at lower replacement levels. The development of the heat of hydration with time of the concrete mixes under adiabatic condition is expressed in equation form.

10.14359/4116


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