The resistance to a 0.5% sulfuric acid solution of six different concrete compositions with and without addition of polymer was investigated. Four different polymer types were used: a styrene-acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer. The different concrete compositions were tested on a testing apparatus for accelerated degradation tests. The test procedure consists of an alternated submersion in a 0.5 % sulfuric acid solution and drying in air of the test cylinders (0 230 mm, height 70 mm). After each cycle, the concrete cylinders were brushed with rotary brushes to remove the weakly adhering concrete particles. Concrete degradation was measured by the change in radius of the cylinders after each cycle. The measurements were performed before and after brushing in order to determine the swelling of the cylinders due to sulfate attack formation of gypsum and ettringite- as well as the decrease of the radius due to material loss caused by brushing. The concrete composition with blast furnace slag cement showed the best resistance to the sulfuric acid attack. Comparing the four different polymer types, addition of styrene-acrylic ester increased the resistance of the concrete the most. The addition of the acrylic and the styrene butadiene caused a decreased resistance of the concrete compared to the composition without polymer addition.

In order to obtain specific concrete properties for distinct applications on site, the use of blends of different admixtures should be considered. During the construction of a roadway bridge, with long and large piles in an aggressive chemical environment, a comparative study was made to analyse the effect of blending of a melamine-based superplasticizer with triethanolamine-based admixtures, and polycarboxylate with lignosulphonate-based admixtures by the other side, on the slump loss of a flowable concrete. The performance of a mixture of plasticizer/superplasticizer was compared with that obtained by the single use of the individual admixtures. A naphthalene sulphonate-based admixture was also investigated. The results show that blending of modified lignosulphonate with polycarboxylate based admixtures in lower dosages, produces a significant synergistic action that provides improvements on slump-loss, with only a small delay in the initial setting time. With polycarboxylate based admixtures it is possible to get significant slump retention without compromising the early strengths

Carboxylic acid ester superplasticizers (CAE) consist of polymers in which hydrophilic polyoxyethylene ester chains (CE) are grafted onto a main chain bearing carboxylic groups (CA). In the present work, CAE copolymers characterized by different molar carboxylic acid - carboxylic ester ratios (CAKE) were synthesized and evaluated as super-plasticizers by using two different cements. The efficiency of CAE copolymers as superplasticizers was found to be dependent on the carboxylic acid - carboxylic ester ratio (CAKE) and the optimum CA/CE value in order to attain the best flowability was different for the two cements. Adsorption measurements indicated an increase of adsorption onto both the cements by increasing CAKE. On the other hand, zeta potential of cement pastes was not substantially influenced by the addition of the different superplasticizers. The results of the present work seem to indicate that both adsorption and steric stabilization are the main factors which determine the performances of CAE as superplasticizers and that CA/CE is an important parameter influencing the cement/CAE superplasticizer compatibility.

A new conductivity method is proposed to monitor the behavior of fresh cement-based materials during the consolidation, setting, and early hardening periods. The method relies on differences in electrical conductivity measured at different depths, and as function of time, to evaluate variations in the local composition (solids, fluids) of the material. To perform these measurements in a practical and cost-effective way, simple disposable conductivity probes were designed with multiple electrodes, after initial work with similar laboratory-type probes. The approach was tested with several cement-based systems ncluding grouts, mortars, and concrete. During the dormant period, the conductivity readings reflect changes in the homogeneity of the samples as a function of time, which are qualitatively well related to the bleeding-segregation behavior of the cement-based system. From the conductivity data obtained as a function of sample depth, a stability index could be defined using the least-squared deviation from the mean conductivity at a given time. The time-dependence of such a stability index reflects the evolution of the bleeding and segregation phenomena in the material. The multi-electrode conductivity approach also yields other valuable information, namely a determination of the initial setting, and a reasonable estimate of the rate of strength development during the early stages of the hardening period.

Total and external chemical shrinkage have been followed for a number of cement pastes until 48 h. Total chemical shrinkage is believed to roughly be proportional to degree of hydration, while the differences in external chemical shrinkage give an impression on how prone the mixture may be to micro-cracking. The difference between total and external shrinkage result in contraction pores. This study is part of a larger on-going study focusing on the early volume change of binders of high performance concrete. Variables in the present part of the study have been plasticizer (sodium lignosulphonate) and super-plasticizer (sodium salts of sulphonated melamine -formaldehyde condensate and naphthalene sulphonate - formaldehyde condensate) and water-to-cement ratio (0.30, 0.35, 0.40, 0.45 and 0.50). A few mixes were also made with a combination of plasticizer/super-plasticizer, a common practical concept. The total plasticizer/super-plasticizer dosage was 1% by weight of cement, and the cement chosen was a high strength portland cement commonly used for high performance structures. Total chemical shrinkage could be used to monitor the retardation of the cement setting by for instance lignosulphonate and the acceleration of hydration rate thereafter. The hydration development of pastes with plasticizers (LS) or super-plasticizers (SNF and SMF), as measured by total chemical shrinkage, seems virtually independent of the water-to-cement ratio in the range 0.30-0.50 during the first 48 hours. Only the hydration for the paste with the lowest w/c may be slightly accelerated immediately after setting, but reached slightly lower values at 48 h. Lignosulphonate (LS) retard setting more than the super-plasticizers naphthalene sulphonate - formaldehyde condensate and sulphonated melamine - formaldehyde condensate. The flattening-out-level of the external chemical shrinkage was only marginally influenced by w/c, with non-systematic individual differences being in the order of 0.1 ml/l00 g cement. The flattening-out- level of the external chemical shrinkage was independent of admixture type at w/c = 0.40, and the same as the reference without admixtures.