International Concrete Abstracts Portal

Original Reactive Powder Concrete (RPC) - in form of a superplasticized cement mixture with silica fume, steel fibers and ground fine quartz (150-400 pm) - was studied in comparison with a modified RPC where a graded natural aggregate (max size 8 mm) was used to replace the fine sand and/or part of the cementitious binder. Original and modified RPC were manufactured at a plastic-fluid consistency, cast by vibration and cured at three different conditions: a) room temperature; b) steam-curing at 90°C; c) high pressure steam-curing at 160°C. The addition of the graded aggregate does not reduce the compressive strength provided that the quality of the cement matrix, in terms of its water-cement ratio, is not changed. This result is in contrast with the model proposed to relate the high compressive strength level of RPC (200 MPa) to the absence of coarse aggregate. Both the original and modified RPC (with the coarse aggregate addition) perform better - in terms of higher strength and lower driying shrinkage or creep strain - when they are steam cured rather than cured at room temperature. This improvement was related to a more dense microstructure of the cement matrix, particularly in the RPC specimens steam cured at 16OOC.

SP173 In October 1997, the Council for the Orginazation of CANMET/ACI Conferences in association with American Concrete Institute and several cement and concrete organizations in Italy sponsored the fifth conference on the subject in Rome, Italy. This conference was aimed at transferring technology in the fastmoving field of chemical admixtures. A total of more than 60 papers from more than 20 countries were received and reviewed by the ACI review panel and 49 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI special publication SP-173.

An acrylic polymer was mixed with fine sand and cementitious binders. The mixtures were studied as rubber-like coating to protect reinforced concrete specimens. Three coatings (all with water-binder ratio of 0.50, polymer-binder ratio of 0.50 and sand-binder ratio of 2) were produced by changing the type of binder: portland cement, pozzolan-portland cement with metakaolin and slag-based cement. The coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on uncoated and coated concrete specimens were carried out to study the penetration of water, carbon dioxide, chloride, and sulphate ions. The resistance to penetration of these aggressive agents was very poor in the uncoated specimens and became as good as that of a watertight and durable concrete in the coated specimens. Coated beam specimens were kept for 24 months in three different environments (laboratory at 20°C and 60% R.H.; outdoors environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the binder type on the bond strength and the flexibility of the coating in terms of ability to bridge the cracks of the concrete substrate. Bond strength of the coatings was substantially unchanged or improved by the exposure to the three different environments. Initial flexiiity of the coating was improved by the addition of metakaolin or slag. However, at later ages there was some flexibility loss, for coated concrete specimens exposed to water, when portland cement was used specially in the presence of mtakaolin. No flexibility loss was found in the polymer-cement coating in the presence of slag.

The authors have shown that it is possible to make a concrete with low-heat and high-strength by properly exploiting the potentials of the materials used. The high-range water-reducing air-entraining agent (AE) used played an important role. However, there was a need to reduce the slump loss. A new high-range water-reducing AE agent was developed for this purpose. The agent is a compound of a polycarboxylate type copolymer and a special polymetric surface active agent. This paper describes strength and heat properties of concrete with the developed agent. A moderate heat portland cement and a super-ground granulated blast-furnace slag were used. The test results showed that the newly-developed high-range water-reducing AE agent makes it possible to reduce the slump loss of concrete without losing the properties of low-heat and high-strength. However, it was found that the low-heat property of the developed concrete is lost when the concrete is proportioned to be flowable.

In this work a paste viscometer with concentric cylinders is used to evaluate the mineral- and chemical admixtures’ impact on fresh fine mortar rheology. Rheology results have been evaluated according to the Bingham model, which describes the rheology with the parameters; yield stress and plastic viscosity. Seven dolomite fillers have been investigated in combination with one superplasticizer and two cement types. The fillers originate from the same deposit, i.e. having the same mineralogy but different particle size distribution. Relationships have been established between rheology results and particle size analysis of cements and fillers. Increasing fineness leads to higher yield stress and plastic viscosity. Addition of superplasticizer results in a parallel displacement of these relationships towards lower rheology values. The results also show a significantly large difference in rheology depending on type of cement. Rheologically, the finer cement exhibits lower yield stress and plastic viscosity than the coarser cement, when adding the same amount of filler. The results for the reference mixes, when no filler is added, are the opposite. Rheology tests using a paste viscometer with concentric cylinders on the fine mortar part of the concrete is a effective method to describe additives’ influence on fresh concrete rheology.