International Concrete Abstracts Portal

Norida Department of Transportation (FDOT) requires contractors to submit proposed concrete mixture proportions prior to the production of any concrete. The contractor must use mixture proportions approved by FDOT. Substitutions of ingredients, other than coarse aggregate, must be justified through trial mixtures, and authorized in writing by FDOT Engineers. The substitutions of fly ash, slag, air-entraining admixtures, and 'I).pcs A, D and G water reducing admixtures were performed on two typical FDOT hot weather mixture proportions in this study. The concrete properties considered were slump, air content, and compressive strength. Test data for substitution mixture propohons were compared with the data for the original mixture proportions on the basis of statistical criteria. Results show that the substitutions cause significant change in concrete properties for the fly ash mixture proportions. The substitution of slag and air-entraining agent in the slag mixture proportions does not cause significant change in the properties of concrete.

Numerical and experimental studies or Keactive rowaer doncrete (RPC), reinforced by short steel fibres, under biaxial tensile loading are reported. A semi-analytical model using the Eshelby’s method of inclusion to describe elastic fields perturbation is employed to predict crack nucleation under biaxial tensile strain. A criterion of crack nucleation is investigated theoretically by considering a locally oriented mass of fibres embedded in an homogeneous matrix. An original biaxial crucifonn specimen is designed and fabricated by a systematic testing program guided by the results of a numerical simulation. A prototype machine names ASTREE (developed by SCHENCWLMT) is used in the biaxial test of cruciform specimens. An adaptive control test method was designed, and digital image correlation is employed to obtain the displacement field and the microstructural stress concentration. These preliminary observations support our theoretical analysis based on Eshelby’s inclusion and aims at a better understanding of the mechanisms involved in the RPC damage process.

The behavior of liquid containing structures (LCS) subjected to seismic excitations is reviewed. The major parameters affecting the response of concrete circular tanks for LCS are discussed. Existing codes aud standards related to seismic design of LCS are reviewed. With the aid of a design example, results of the various design standards are compared. The effects of earthquake load on the behavior of reinforced concrete (RC) tanks are also investigated through a detailed example.

Cast-in-place deep foundations such as drilled shafts and piers are often subjected to two sources of problems. First, the integrity and uniformity of the cross-sectional area of these structural elements cannot be assured using normal concrete because of limited accessibility and visibility during construction. Cavities and soil encroachments leading to soil pockets can jeopardize their load-bearing capacity. Second, corrosion problems of steel reinforcement in deep foundations have been costly, requiring annual repair costs of more than $2 billion in the US alone. To address these two challenges, a novel technology for the construction of drilled shaft concrete piles is proposed in this study. Self-consolidating concrete, a material that compacts under its self-wight without vibration and without bleeding or segregation, is used to assure the structural integrity and uniformity of the cross-sectional area of deep foundations. The self-consolidating concrete is cast into FRP envelopes, which provide corrosion-resistant reinforcement. This paper presents results of a laboratory investigation on the mechanical performance of these novel piles including the effect of using expansive cement and shrinkage-reducing admixtures to enhance the FRP tube-concrete interfacial bond.

The objective of this research was to verify the feasibility of reducing the drying shrinkage of concrete made with portland pozzolan cement. Major variables included slump, shrinkage-reducing admixture brand, admixture dosages and specimen dimensions. Tests were carried out on 132 prism specimens and shrinkage strain8 were measured up to 360 days of drying. Also compressive strength, splitting strength and static modulus of elasticity were determined. Based on the results obtained, it was concluded that dl of the five brand admixtures evaluated reduce drying shrinkage. One Qf the experimental admix- tures exhibited the best behavior and reduced up,k, 45% of the average free shrinkage of concrete at 360 days of drying. Results were compared with drying strain predictions of ACI, CEB, B3, GL, Sakab and Sakata 2001 models. It was conduded that in general a l l the ana- lyzed shrinkage models do not adequately represent the observed shrinkage behavior of concretes made with portland pozzolan cement and shrinkage-reducing admixtures. Therefore, two prediction models to estimate drying shrinkage strains were developed based on the ACI drying-time function and Sakata’s ultimate shrinkage strain. One of these models is for use at a design level when no information about a particular shrinkage reducing admixture is known, and the other is applicable to concrete made with a particular admixture brand.