International Concrete Abstracts Portal

A high performance concrete (HPC) mixture was developed in the laboratory and later used in a bridge construction project. The HPC mixture was designed based on 752 lb (341 kg) of cement with 0.33 water-cement ratio. The weight of the cement was partially replaced by fly ash (20 percent) and silica fume (8 percent). The concrete mixture incorporated 4.5 gal./yd 3 (22.3 L/m 3) of calcium nitrite corrosion inhibiting admixture. Other chemical admixtures included air-entraining agent, and/or standard and high range water-reducing/retarding admixtures. A wide range of field and laboratory tests were performed on fabricated concrete specimens, as well as on cores from field models and newly cast bridge members. The main tests included field and laboratory testing of permeability, and compressive strength. Results of tests on laboratory and field concrete were very close. The chloride permeability AASHTO T277) of the HPC was very low, ranging between 618 to 1055 coulombs. The compressive strength was high, ranging between 8600 to 10,670 psi (59 to 74 MPa). This study shows that laboratory produced HPC with multiple cementitious materials and chemical admixtures can be successfully implemented in construction without compromising its durability. It is also demonstrated that sacrificial concrete models cast and cured at the job site can provide accurate evaluation of the durability and performance of newly cast structures. The study also emphasizes the need to test the permeability as well as strength for more precise assessment of concrete durability.

We developed an enhanced flowable concrete using both a binary low-heat cement and coarse aggregate of 40 mm maximum size, usable in large-scale mass concrete structures (this concrete is provided with a high flowability and an excellent resistance to segregation, and is able to be placed densely without compaction). We verified that its fundamental performance surpasses that of existing types of concrete. Further, we also verified that it possesses superior workability when compared with conventional concrete. Next, we established production, quality control, and construction methods for super-workable concrete through experiments at a large scale construction site, and utilized it in a large-scale structure. We were able to verify the following results: superior workability of the concrete because it can be spread and compacted easily; effective control over thermal cracking because concrete temperature rose very little. Furthermore, the hardened concrete is confirmed, from the core samples, to be very compact and has excellent strength. 161-493

The cable-stayed bridge which is being built across the Elorn river near Brest (western France) will have the world's longest span (400 m, or 437 yd) in this range of full concrete bridge. Besides a normal-strength concrete (C 35/6,500 psi), a lightweight concrete (LC 32/4,600 psi) is extensively used in the deck, in order to minimize the effect of dead load on the overall stability. But the most significant part of the loads to be carried by the bridge is due to the wind, with a maximum accounted speed (in the design) of 210 km/h (130 mph). Furthermore, the bridge is located about 3 km (2 miles) from the sea; thus, the wind will carry a large amount of chlorides. This is why the term serve environment seems to be appropriate for the Elorn bridge. Two grades of high-strength concrete--namely C60/ psi and C80/ psi--are used in the towers. For the first time in France--and perhaps in the world--a strength of 80 MPa (11,600 psi cylinder strength) has been used in the design of a bridge. Details on the concrete mix proportions, producing facilities, placing techniques and testing of samples are given in this paper. A special emphasis is put on the thermal curing aspects. As the thickness of the towers walls is 1.10 m (3.5 ft), the temperature can reach more than 80 C in the pylons. The effect of heat of hydration on the long-term strength and modulus was investigated. Also, finite-element calculations were performed, in order to predict the stresses induced by thermal gradients, and to choose the most appropriate curing (thermal insulation, time of form removal, and so on).

In 1989, the Strategic Highway Research Program contracted with North Carolina State University to investigate the use of High Performance Concrete in highway applications. A major goal of this research project was to determine if HPC mixtures could be successfully produced in the field. In addition, an evaluation was to be made of the long-term performance of this material under field service conditions. Five field installations were constructed around the country for this purpose. The fresh and hardened properties of the concrete were found to be generally acceptable at each site. Some cracking has developed in a few sections. A set of recommendations with regard to the use of HPC in the field was developed as a result of the field work.

Three types of High Performance Concrete (HPC) for highway applications were investigated: Very Early Strength (VES), High Early Strength (HES) and Very High Strength (VHS). Two of the objectives of the research were to measure the chloride permeability of these concretes and explore an alternate method using AC impedance. Many of the concretes had coulomb values of 4000 and higher, placing them in the "high permeability" category as specified by AASHTO T 277 - Rapid Chloride Permeability Test (RCPT). Coulomb values were also found to decrease with concrete age and with increased silica fume content. Coulomb values were found not to vary significantly with dosage of calcium nitrite used as accelerator, up to 6 gal/yd 3 (29.7 l/m 3). The AC impedance test results (ohms) were found to correlate well with the RCPT results (coulombs) and were sufficiently accurate to place the concretes in the proper chloride permeability category. The advantages of the AC impedance test are that it is faster and less expensive than the RCPT and it avoids the potential heating problem sometimes encountered in the RCPT. AC impedance was found to increase with concrete age and with increased silica fume content and decrease with increased calcium nitrite dosage.