International Concrete Abstracts Portal

SP-217 This Symposium Publication includes 39 papers selected from the conference that took place in Berlin, Germany, in October 2003. Topics include cold-weather concreting, durability, polycarboxylate and polycondensate, self-compacting concrete and much more.

Three new polycarboxylate-based liquid superplasticizers (SPI-3) and powder superplasticizers (PSPI-3), which are made from SPI-3, are synthesized and evaluated. SP3, which has two different lengths of polyoxyethylene chains in one polymer molecule, showed high cement dispersing capability, good fluidity retention and short setting time. PSP3, which is made from SP3, showed low moisture absorption and excellent antiblocking property. The results show the following properties of PSP3, compared to those of general powder type superplasticizers such as Naphthalene-based powder superplasticizer (NS) and Melamine-based powder superplasticizer (MS). 1) Necessary dosage to obtain equal fluidity is about a tenth. 2) Fluidity retention is better. 3) Setting time is shorter. 4) Compressive strength of mortar is higher. 5) PSP3 is non-formalin type superplasticizer.

Recently, due to demands for higher strength and retention of flowability in concrete, polycarboxylate-based superplasticizers (PC) have attracted much attention. Polycarboxylate-based superplasticizers above all, have been recognized to show superior water reducing ability and ability to retain workable consistence. PC has also been an indispensable material for various kinds of high performance concrete, especially for making extremely low water-cement ratios (W/C) possible. Because of a shortage of quality aggregate in Japan and a need to adhere to the maximum water content regulation for concrete durability in which the upper value is limited to quantities lower than 185kg/m3, the use of PC for water reduction has been increasing. The significance of cracks on the durability of concrete has been pointed out in many studies. In order to reduce the effect of cracks, it is important to reduce the autogenous and drying shrinkage. In light of such concerns, a new multi-function and multi-purpose PC has been invented. PC incorporating both shrinkage and water reducing effects in wide range of W/C; the performance of which is described in this study. This new PC can be applied to numerous scenarios ranging from high W/C to very low W/C requirements. Its multipurpose makes it a candidate for a new generation of superplasticizers.

Recently, ultra high-strength concrete with a specified concrete strength of 100 N/mm2 or more is being applied in Japan. The use of ultra high-strength concrete in the lower stories of high-rise buildings allows the architects to reduce the sectional area of support columns and thus increase floor areas. Other advantages are the suppression of cracking caused by earthquakes, and the increased durability of the concrete structure. In Japan, these ultra high-strength concretes are placed to congested reinforcement point. So, they are required to have high deformability and low viscosity. To produce this kind of concrete having an Fc of 100 N/nun2 or more, the water-cement ratio must be below 25%. Conventional BNS-based high-range water-reducing agents cannot impart high deformability and low viscosity until placement is finished to concrete with low water-cement ratio. Conventional polycarboxylate-based high-range waterreducing agents make the fresh concrete very deformable; however, the viscosity of the concrete increases, resulting in high loads when pumping and subsequent poor placing ability. It is clear that a new high-range water-reducing agent that imparts high deformability and low viscosity to the concrete is needed. A newly developed high-range water-reducing agent (SPN) imparts high deformability and low viscosity to the concrete until placement is finished. The authors compared the viscosity reducing effects of SPN and conventional polycarboxylatebased high-range water-reducing agent in concrete.

The shrinkage of concrete originates stresses on restrained structural elements, which can cause cracks. In some cases, for instance to reduce the number of structural joints, it is important to decrease drying shrinkage by the use of a shrinkage reduction admixture (SRA). The effectiveness of a SRA depends on porosity and stiffness of concrete. In order to evaluate the performance of two SRA products, shrinkage tests have been done on concretes with and without SRA. Two different concrete mixtures were evaluated: a low strength concrete mixture (for housing purposes) and a medium strength concrete mixture (use in bridges). Results show the effectiveness of the SRA on the two reference concrete mixtures, with different W/C and different cement contents.