Role of PVOH and kaolin on colloidal stability of liquid and powder EVA and SB latexes in cement pore solution

Bonding Behaviour of Steel Fibres in UHPFRC Based on Alkali-Activated Slag

The mechanical performance of fibre-reinforced ultra-high-performance concrete based on alkali-activated slag was investigated, concentrating on the use of steel fibres. The flexural strength is slightly higher compared to the UHPC based on Ordinary Portland Cement (OPC) as the binder. Correlating the flexural strength test with multiple fibre-pullout tests, an increase in the bonding behaviour at the interfacial-transition zone of the AAM-UHPC was found compared to the OPC-UHPC. Microstructural investigations on the fibres after storage in an artificial pore solution and a potassium waterglass indicated a dissolution of the metallic surface. This occurred more strongly with the potassium waterglass, which was used as an activator solution in the case of the AAM-UHPC. From this, it can be assumed that the stronger bond results from this initial etching for steel fibres in the AAM-UHPC compared to the OPC-UHPC. The difference in the bond strength of both fibre types, the brass-coated steel fibres and the stainless-steel fibres, was rather low for the AAM-UHPC compared to the OPC-UHPC.

Effect of Polymer Additives on the Microstructure and Mechanical Properties of Self-Leveling Rubberised Concrete

The materials based on concrete with an addition of rubber are well-known. The interaction between concrete components and rubber particles is in the majority cases insufficient. For this reason, different substances are introduced into concrete-rubber systems. The aim of this paper is to establish the influence of five different polymer additives, i.e., 1. an aqueous dispersion of a styrene-acrylic ester copolymer (silanised) (ASS), 2. water dispersion of styrene-acrylic copolymer (AS), 3. anionic copolymer of acrylic acid ester and styrene in the form of powder (AS.RDP), 4. water polymer dispersion produced from the vinyl acetate and ethylene monomers (EVA), 5. copolymer powder of vinyl acetate and ethylene (EVA.RDP)) on the properties of the self-leveling rubberised concrete. Scanning electron microscopy has allowed to establish the interaction between the cement paste and rubber aggregates. Moreover, the compressive strength and flexural strength of the studied materials were evaluated. The results indicate that the mechanical properties depend extensively on the type as well as the amount of the polymer additive introduced into the system.

Concrete Strengthening by Introducing Polymer-Based Additives into the Cement Matrix-A Mini Review

The modern types of concrete are a mixture of aggregates, cement, water and optional additives and admixtures. In particular, polymer additives seem to be a promising type of component that can significantly change concrete and mortar properties. Currently, the most popular polymer additives include superplasticizers, latexes and redispersible powders. Moreover, in order to improve the properties of concrete-based composite admixtures, which enhance the resistance to cracking, polymer fibres and recycled polymers have been researched. All the types of polymeric materials mentioned above are broadly used in the construction industry. This work summarizes the current knowledge on the different types of popular polymeric additives. Moreover, it describes the correlation between the chemical structure of additives and the macro-behaviour of the obtained concrete.

Fluorescence Microscopy of Superplasticizers in Cementitious Systems: Applications and Challenges

In addition to the desired plasticizing effect, superplasticizers used in high and ultra-high performance concretes (UHPC) influence the chemical system of the pastes and for example retardation of the cement hydration occurs. Thus, superplasticizers have to be chosen wisely for every material composition and application. To investigate the essential adsorption of these polymers to particle surfaces in-situ to overcome several practical challenges of superplasticizer research, fluorescence microscopy is useful. In order to make the superplasticizer polymers visible for this microscopic approach, they are stained with fluorescence dyes prior the experiment. In this work, the application of this method in terms of retardation and rheological properties of sample systems is presented. The hydration of tricalcium oxy silicate (C₃S) in combination with different polycarboxylate ether superplasticizers is observed by fluorescence microscopy and calorimetry. Both methods can identify the retarding effect, depending on the superplasticizer's chemical composition. On the other hand, the influence of the superplasticizers on the slump of a ground granulated blast furnace slag/cement paste is correlated to fluorescence microscopic adsorption results. The prediction of the efficiency by microscopic adsorption analysis succeeds roughly. At last, the possibility of high-resolution imaging via confocal laser scanning microscopy is presented, which enables the detection of early hydrates and their interaction with the superplasticizers.

Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC

The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC).