International Concrete Abstracts Portal

The sulphate resistance of mortar lng a superplasticizer and made with blends Type 10 cement, fly ash and granulated blast slag are compared with similar mortars conta ventional water reducing admixture. Compari made with mortars made with C.S.A. Type 50 c Changes in porosity, weight, length, dynamictain- elasticity and compressive strength of the exposed to alternate soaking and ium sulphate solutions for 300 days are desc lus of specified-Interrelationship of w/c ratio, alkalinity of the medium and porosity as primary factors in sulphate attack on the cement paste were investigated. The results indicate that mixes containing a 30% replacement of normal Portland cement by fly ash or slag and a superplasticizer are comparable to mixes made from sulphate resisting cement in their capacity to resist sulphate attack. The degree of attack noted in the superplasticized mixes was significantly reduced in com-parison with mortars where a conventional water reducing admixture was used.

This paper presents the results of a laboratory investigation of 47 mixes (31 exploratory mixes and 16 replicate mixes) of superplasticized fiber reinforced concrete. All these mixes were studied for the effect of various parameters such as water-cement ratio, cement content, fiber content, air-entraining agent, and superplasticizer dosage on the plastic and hardened properties of concrete. The fresh concrete was tested for slump, flow table spread, vebe time, air-content and unit weight. The hardened concrete was tested for (i) compressive strength, and (ii) static flexural strength including load deflection curves, toughness index, determination of first crack load and determination of post crack strength. The addition of superplasticizer increased the workability of concrete and it was possible to produce workable high strength concretes with low water-cement ratios. Collating enables the fibers to be easily handled and they could be mixed with aggregates without producing "balling" or tangling during mixing. The static flexural test shows that excellent bond had developed between the fibers and the mortar matrix. The load deflection curves indicate that there is a considerable ductile behavior in the superplasticized fiber reinforced concrete. The addition of hooked and collated fibers increases considerably the post-crack load carrying capacity, the toughness, the energy absorbing capacity resulting In a high ductility of the composite material. The serious drawbacks of high strength concrete namely reduced workability and lack of ductility can be eliminated by adding superplasticizers and steel fibers which will dequately increase the workability and the ductility of the high strength concrete.

This work examines the course of the adsorption and the variations in the surface charge observed when monosulphate is dispersed in an aqueous or dimethylsulphoxide solution containing li-gnosulphonate, naphtalene formadehyde condensate and formaldehyde condensate. Melamine The adsorption isotherms obtained by using dimethylsulphoxide of Langmuir type. Are In the aqueous medium adsorption is characterized by a maximum beyond which it decreases. The measurements of Zeta potential carried out on monosulphate dispersed in solutions of the admixtures pointed out a nearly linear increase in the negative charge of the particles up to a value corresponding to the maximum of the adsorption isotherms; beyond this value the potential remains constant. The values of Zeta potential justify the dispersing effect caused by the admixtures due to repulsion among the particles.

More than twenty naphthalene sulphonated formaldehyde condensates have been synthesized with various degrees of polymerization. This was evaluated by viscosity measurements of the polymer in water solution. Polymer adsorption, zeta potential, fluidity and compressive strength of cement mixtures have been examined as a function of the degree of polymerization and the polymer dosage. Polymer adsorption, zeta potential and fluidity increase by increasing the polymer dosage in the range of 0.25 -2.00 % by weight of cement. Polymer adsorption, zeta potential, fluidity increase by increasing the degree of polymerization. However, above a certain degree of polymerization all the above mentioned properties do not change further. Cement particles adsorb the polymer molecules and this causes an increase in the electrical charge on the cement surface. This results in a better dispersion of cement particles and a more fluid system. However, even if there is a certain interaction between fluidity and zeta potential, the latter is not the only parameter controlling the fluidity of the system. At the same water/cement ratio, by increasing the degree of polymerization the strength is, in general, slightly increased and this seems to be related to a better dispersion of cement particles.

The principle of a free orifice rheometer is used in a development of a device for site-tests of consistency of fresh superplasticized concretes. The new test is designed to complement the '2-point' test and to provide an alternative or even to replace the DIN Flow Table (1) test. Full scale prototype of the Orifice Rheometer was constructed and tests confirmed the capacity of the rheometer to detect differences between fresh flowing mixtures. Using an appropriate orifice the sensitivity of the device was sufficient to indicate excessive bleeding or segregation caused by an overdose of an admixture. Influence of factors such as the composition of a mixture, type and dosage of a superplasticizer on the consistency of a fresh flowing concrete and on its retention were also investigated. In its present form the Orifice Rheometer is a simple, rugged and easily portable apparatus which has provided encouraging results from its first site trials.

Generally the flow of fresh concrete is assumed to represent distortion as a Bingham body. In this study, in order to clarify the effects of chemical ad-mixtures on the flow of fresh concrete, rheological values such as the plastic viscosity and yield value (shearing stress) of fresh paste and mortar with superplasticizer were experimentally investigated both with and without vibration, Four types of chemical admixtures, sulfonated naphthalene-formaldehyde condensates, sulfonated melamine-formaldehyde conden-sates, poly-condensed aromatic sulfonate and a conventional water reducing agent (modified lignosulfonate) were used, and various water/cement ratio, sand/cement ratio, and consistencies, with and without chemical admixture, were selected for the mix pro-portions of test samples. The apparatus used in this study was designed to conduct experiments on the rheological phenomenon of fresh concrete under vibration. The frequencies of vibration em-ployed were 0, 100, 120, 150 and 180 Hz with accelerations of 0, 2, 4 and 6g. The plastic viscosity and yield value of vibrating cement paste and mortar through which a sphere moves can be calculated from Stokes's law. The results obtained have provided useful in-formation for identifying the fundamental rheological properties of the plasticizing concrete.

In order to consider the workability of superplasticized concrete, it is necessary first to evaluate rheologically the effect of a superplasticizer on fresh cement paste. The authors conducted a series of experiments measuring the resist-ances met by a sphere in motion at various constant speeds in cement pastes, and calculated their rheological constants. It is indicated that the rheological constant of a paste to which superplasticizer has been added is completely different from that of plain paste and also different from pastes with conventional chemical admixtures, and as a result, the superplasticizer can be rheologically defined. Further, in order to clarify the reason for the comparatively rapid slump loss after superplasticizing, the variations in rheological constants due to elapse of time after mixing of cement paste are measured, and it is found that when the addition of the superplasticizer is delayed, the increase in the yield value (rheological constant) is hastened, and it is thus substantiated that the rate of slump loss of concrete is increased when the timing of superplasticizer addition is delayed.

Normally in hot weather, it is difficult to maintain the workability of concrete containing high-range water-reducing admixtures (H-R W-RA) as the concrete temperatures approach 85 - 90°F(29 to 32oC). The loss of fluidity and workability often occurs within 30 min. after the introduction of the adrnix-ture making placement and pumping very difficult if there are delays. This paper discusses how certain modified H-R W-RA may be used to provide fluidized concrete with prolonged work-ability.

a few as Ca-acid, concre Of the slump in mor Superpla hours. The e lignosulfonat Na-heptonate te containing se admixtures loss; the inf tars was also sticized concrete 1 ffect of different , sucrose, Na-glut and Na-boroheptonat sulfonated melamin Na-gluconate prov luence on setting t examined. oses its workability within amounts of admixtures, such onate, citric acid, salicylic, on the slump loss of formaldehyde is reported. to be the best retarder of times and strengthdevelopment

Today, the developing countries have sufficient techni-cal manpower and basic research facilities to develop indigenous know-how for most chemicals. As far as superplasticizers are concerned, Gas-layer Chromatographic equipment, Infra-red/Ultra-violet spectrometers and a well equipped analytical chemical laboratory are adequate to develop know-how indigenously. The paper describes such development work which has been successfully done in India. Such production of superplasticizers is essential to developing countries where cement shortages and poor quality cement seriously hamper construction work of large and essential projects.