ABOUT THE INTERNATIONAL CONCRETE ABSTRACTS PORTAL

  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal

Showing 1-5 of 50 Abstracts search results

Document: 

SP173-14

Date: 

September 1, 1997

Author(s):

L ICoppola, C. Pistolesi, P. Zaffaroni and M.Collepardi

Publication:

Symposium Papers

Volume:

173

Abstract:

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.

DOI:

10.14359/6188


Document: 

SP173-38

Date: 

September 1, 1997

Author(s):

A. I. Vovk, G. A. Vovk and A. V. Usherov-Marshak

Publication:

Symposium Papers

Volume:

173

Abstract:

Results describing investigations of the kinetics of hydration and struc-ture formation of cement systems (C3 S, C3 A, C3 A + gypsum, and portland ce-ment) in the presence of naphthaleneformaldehyde type superplasticizers (SNF ) of different compositions are discussed Using the individual components of SNF sodium polymethylenenaphthalenesulfonates ( PNS ) with polycondensation degrees ranging from 2 to 17, the basic dependences of the kinetics of the processes on the average molecular mass of the admixture ( Mn were shown In the case of C3 S the retarding effect of SNF on hydration and structure formation processes depends lineally on Mn , as a general rule, whilst for C3 A the retarding effect is more pronounced for mid-condensated components of superplasticizer. This difference is due to the different adsorption mechanism of the superplasticizer on the above-mentioned minerals. The unusual form and the analogy of ther-mokinetic curves for C3 A and C3 A - gypsum hydration in the presence of PNS are the first experimental proof that organic-mineral compounds are formed in these systems.

DOI:

10.14359/6212


Document: 

SP173-13

Date: 

September 1, 1997

Author(s):

J.J.Brooks and X.Jiang

Publication:

Symposium Papers

Volume:

173

Abstract:

A consequence of drying shrinkage is intrinsic cracking due to some form of restraint. In thick sections of concrete, drying from the surface causes differential shrinkage and such internal restraint can be responsible for surface cracking because of the induced tensile stress. When thin drying concrete members are restrained externally, a time-dependent failure is likely unless drying shrinkage is minimised. Besides drying shrinkage, the potential for cracking depends on tensile creep and tensile strength or tensile strain capacity and such properties are not normally measured in the laboratory. The possible effects of chemical admixtures on the foregoing properties is also largely unknown. The current research is investigating the role of tensile creep in relieving the tensile stress induced by fully restraining the drying shrinkage of concrete with and without chemical and mineral admixtures. All the relevant properties contributing to the time-dependent strength are being measured using bobbin-shaped specimens previously developed for uniaxial creep determination. The present paper presents the findings for concretes with and without a plasticizer and a new shrinkage reducing admixture. While the plasticizer has little influence on properties, the shrinkage reducing admixture significantly lowers the strength, elastic modulus, free drying shrinkage and creep. When restrained from the age of seven days all the concretes failed between 4 and 13 days, the concrete with the shrinkage reducing admixture failing at the lowest stress but after the longest time.

DOI:

10.14359/6187


Document: 

SP173-32

Date: 

September 1, 1997

Author(s):

E. Tazwa, B. Mtasiwa and M. Takahasi

Publication:

Symposium Papers

Volume:

173

Abstract:

This paper reports the properties of cement paste, mortar and fresh and hardened concrete using superplasticizers with electric repulsion, steric barrier and those possessing both dispersing mechanisms and their interaction with cementitious materials having pozzolanic properties and those without pozzolanic properties prepared by different mixing methods. It was found that there is an a optimum W/C for the primary water (Wl/C) where bleeding is minimum and thus dispersion state is optimum. The fresh properties of concrete prepared by double mixing method are different from those by conventional mixing method (Single mixing). Also, when superplasticizers are added in primary water (WI), fresh properties of concrete are different from those when added in secondary water (WZ). The effect of dosing method of superplasticizers and replacement of cement with different cementitious materials, varies greatly with the type of superplasticizers.

DOI:

10.14359/6206


Document: 

SP173-16

Date: 

September 1, 1997

Author(s):

P. Billberg

Publication:

Symposium Papers

Volume:

173

Abstract:

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.

DOI:

10.14359/6190


12345...>>

Results Per Page