Both shrinkage reducing admixtures (SRA) and expansive admixture (EXP) can be used to reduce the risk of cracking in concrete. Synergistic effect of using both of those admixtures simultaneously was a was found, however little information can be found on the effects of using both EXP and SRA on the properties of mortars and concrete other than shrinkage. Therefore in this paper, effect of adding both EXP and SRA on properties of mortars outside of their effect on shrinkage is researched. Mortars with Portland cement CEM I were modified by adding EXP and SRA in amount of full dose recommended by the producer, and half of the recommended dose. Research consisted of tests of properties of fresh mortars (consistency, initial setting time, hydration heat) and hardened mortars (compressive strength and drying shrinkage). It has been found that using both SRA and EXP admixtures leads to maintaining the same setting time which can be prolonged if only SRA is used, decreased compressive strength, possibility of increased consistency. Synergistic effect on shrinkage was also confirmed.

Domieszkowano do ceramiki odpadowy szlam pogalwaniczny z ołowiowania fluoroboranowego, zawierający oprócz 60,7% ołowiu 3,7% fluoru (w przeliczeniu na pierwiastki). Kształtki z domieszkami 1, 2, 3 i 10% szlamu wypalone w temperaturze 980°C poddano badaniom fizykomechanicznym (pod względem skurczliwości, nasiąkliwości, mrozoodporności, wytrzymałości na ściskanie) oraz próbom wymywalności wodą nasycaną dwutlenkiem węgla. Badania wykazały, że dodatek 1% szlamu nie zmienia własności wyrobów, a wymywalność ołowiu i fluoru nie stwarza zagrożenia. Wyższe domieszki w miarę ich zwiększania pogarszają wskaźniki jakościowe. Podczas wypalania występuje emisja fluoru do gazów odlotowych.

This article presents test results of cement paste and binders with admixture of hydrophilic or hydrophobic nanosilica. The aim of the study was to determine the influence of nanosilica type and mixing method on compressive strength, porosity, and bulk density of cement paste, also on hydration heat of cement binders. The binder compounds were mixed in high speed mixer in order to provide the highest possible dispersion of nanoparticles in the binder before adding it to mixing water. Two mixing methods were studied. The admixtures increased the reactivity of cement binders. Both nanosilica types increased early compressive strength by 25% in comparison with control series. The increase in 28-day compressive strength was observed with the admixture of hydrophilic nanosilica. The differences in dynamics of binders rate of hydration and development of cement pastes compressive strength denote different reaction mechanisms of both types of nanosilica. Application of higher rotation speeds does not guarantee satisfactory mixing of the binder components. For compressive strength enhancement of cement paste prolonged mixing time occurred to be more important.

For the decreasing of too high air volume in SCC, application of anti-foaming admixture (AFA) is proposed. In effect, AFA is increasing mix flow diameter and decreasing the flow time. Moreover, the workability loss is lower. In case of mix incorporating AFA, their high fluidity do not generate segregation of the mix, which is possible in case of SCC incorporating only SP. The effect of AFA application on the compressive strength depends on the proportions between SP and AFA. AFA has not a negative influence on the freeze-proof properties of the tested concrete. The advisable influence of AFA on porosity characteristic of SCC is proved by research results according to EN 480-11 code.

Admixtures are commonly used nowadays in the mix composition of concrete. These additions affect concrete properties and performance especially creep deformations. This paper shows the effect of admixtures on creep of concrete. In fact, creep deformations have prejudicial consequences on concrete behaviour; an incorrect or inaccurate prediction leads to undesirable consequences in structures. Therefore, an accurate estimation of these deformations is mandatory. Moreover, design codes do not consider admixtures’ effect while predicting creep deformations, thus it is necessary to develop models that predict accurately creep deformations and consider the effect of admixtures. Using a large experimental database coming from international laboratories and research centres, this study aims to update the Eurocode 2 creep model by considering the type and percentage of admixtures using Bayesian Linear Regression method. The effect of two types of admixtures is presented in this paper; the water reducer and silica fume.

The properties of expansive concretes made of two types of cement: Portland cement CEM I and blast furnace slag cement CEM III were tested. The expansion of the concrete was caused by using an expansive admixture containing aluminium powder added in an amount of 0.5; 1 and 1.5% of cement mass. It was found that the compressive strength of concrete with CEM I decreased after using an expansive admixture in the amount of more than 0.5% of the cement mass. The compressive strength of concrete with CEM III decrease after addition of admixture in the entire range of dosages used. On the basis of electrochemical measurements, it was found no influence of an expansive admixture on corrosion of reinforcing steel. The use of an expansive admixture causes a slight increase in the effective diffusion coefficient of chloride ions in concrete.

Self-Compacting Concrete (SCC) has been widely used in the filling layer of high-speed railways. The quality of the filling layer directly affects the durability, comfort, and safety of the track system. In this study, shrinkage characteristics and the creep behavior of SCC were investigated by compressive creep tests and shrinkage tests. They were performed on specimens with different loading levels with a calcium sulfoaluminate-based expansive agent (UEA) and viscosity modified admixture (VMA). Furthermore, based on the scanning electron microscope (SEM) morphology of hydration products and X-ray diffraction (XRD) analysis, the influence of admixtures on microstructure and mineral phases of SCC was analyzed.The results show that when concretes were loaded with the same stress level, the main factor influencing creep of SCC was the quantity and microstructure of amorphism and hydration crystal. The XRD and SEM result showed that UEA andVMAmake the creep and shrinkage of SCC reduce obviously as the cementitious system grow many crystals in hydration products. The creep of NC was less than SCC with identical compressive strength. At the same time, the addition of UEA can improve the ability to resist drying shrinkage.