The Influence of Different Pre-Treatments of Concrete Surface on the Bond Strength of Geopolymer-Type Coating Layer

The treatment of concrete surface using more durable material is one way to slow down the damage process of material, which can negatively affect durability of construction. This paper is aimed at testing the geopolymer-type coating materials of different composition while placing emphasis on various techniques of surface pre-treatments of concrete to which they were applied. The main composition variables were as follows: the fly ash fineness (original, ground) and the addition of washing-aggregate sludge. Four compositions were tested and compared with the composition based on cement binder. The cement mixture was prepared using the same fillers. The following techniques of surface pre-treatment of concrete were applied: brushing, pressure washing, and pressure washing followed by penetration, together with non-treated surface being used for comparison. The effect of the surface treatment technique was tested through the adhesion strength, which was executed at 2, 7, 28, and 120 days after application of the coating. The influence of the composition of geopolymer coating material was also discussed. Geopolymer-based mixtures achieved better adhesive strength than the cement-based mixture, regardless of surface treatment technique. The addition of sludge microfiller seems to be beneficial in improving the adhesive strength of geopolymer-type coating material

The Effect of Mixing Technique and Prolonged Mixing Time on Strength Characteristics of Concrete

The experiment aims to test the triple mixing (3M) technique to produce the concrete with recycled concrete aggregate (RCA). Then, the impact prolonged mixing, representing the influence of delivery and discharge time in praxis, is analysed by the change in strength properties. Both the 28-day compressive strength and tensile splitting strength are evaluated in two aspects: the prolonged mixing time (0, 45 and 90 min after initial mixing), and the mixing method (normal and triple). Prolonged mixing time brought both the positive and negative changes in strength characteristics however the worst difference between initial mixing (0′) and 90′ minutes of mixing was only 8.4% for compressive strength and 8.5% for tensile splitting strength

Analysis of compressive strength of concrete prepared by triplemixing technology depending on both the discharge and curing time

Compressive strength of concrete having recycled concrete aggregate is influenced by the properties and amount of those aggregate. The worse quality of RCA can be eliminated by specific mixing approach. Practical mixing and delivery of concrete could affect the properties of ready concrete due to prolonged time. In this paper, both the fly ash and fine fraction of recycled concrete were used to improve the quality of concrete due to coating of RCA, while the triple mixing technology was applied for this purpose. The compressive strength is evaluated from two aspects: the curing time (2, 28 and 90 days) and discharge time (0, 45 and 90 minutes after mixing) with attention being paid to the type of aggregate and the type of coating material. When using triple mixing technology, prolonged discharge time brings only small effect on the compressive strength (up to 12%) both in positive and negative way, depending on kind of coating material

Evaluation of the Influence of Specific Surface Treatments of RBA on a Set of Properties of Concrete

High water absorption of recycled brick aggregate (RBA) is one of the most discussed parameters in terms of its application in the production of concrete—its influence on the amount of mixing water and, hence, the quality of the concrete, is usually considered negative. In this paper, different methods of decreasing the absorption of RBA and, consequently, the impact on the properties of concrete, are described. The RBA has been treated to decrease the water absorption capacity by impregnation approach using specific impregnators. Afterwards, the RBA samples have been dried at two different temperatures in the laboratory oven—20 and 90 °C. Concretes using 4/8 fraction of the treated RBA instead of natural aggregate (NA) have been mixed and tested. The effectiveness of the RBA treatments have been evaluated on the basis of their influence on the properties of the hardened concrete; by means of the following tests: flexural strength, compressive strength, capillarity, total water absorption capacity, depth of water penetration under pressure, and frost resistance. The method of ranking by ordinal scale has been used as it is suitable for the comparison of a large set of results, while results have been analyzed in terms of the most important technological parameter that influences the quality of the concrete-effective water content. Out of all the tested surface-treatments of RBA, treatment by sodium water glass has the best potential for reduction of the water/cement (w/c) ratio. When the effective w/c ratio is kept within standard limits, concretes containing treated RBA are possible to be specified for various exposure classes and manufacturing in practice. The experiment confirms that at a constant amount of mixing water, with decreasing water absorption of RBA, the effective amount of water in the concrete increases and, hence, the final properties of the concrete decrease (get worse). As the water absorption of the RBA declines, there is a potential for the reduction of the w/c ratio and improvement in the quality of the concrete

Effect of Surface Modifications of Recycled Concrete Aggregate on Concrete Properties

The experiment aims to test the specific way of producing concrete with recycled concrete aggregate (RCA). To reduce its negative impact on the concrete properties, two different ways of treatment of the RCA with geopolymer slurry were applied—coating during the mixing using the specific mixing approach and coating prior to the mixing of concrete. As control samples, a mixture prepared by natural aggregate only and a mixture with RCA that was prepared by standard mixing with no coating process were tested as well. The results of density, total water absorption, and compressive strength in periods of 28, 90, 180, and 365 days of curing are presented and evaluated. Both methods of coating of the RCA with geopolymer slurry allow for the preparation of concrete with properties comparable to those of normal concrete (prepared by standard mixing with natural aggregate); thus, it seems to be a promising way to enhance the rate of RCA application. The positive effect of coating is clearly visible after a longer period of curing (180 days). When comparing the methods of RCA coating, coating directly during the mixing yields somewhat better results; it is also positive from the technological point of view, since the process is simpler in practice

The Influence of Discharge Time, Kind of Additive, and Kind of Aggregate on the Properties of Three-Stage Mixed Concrete

Application of recycled aggregates (RA) for concrete production is limited due to their poor quality. While the environmental benefits of using the RA are well accepted, some unsolved problems prevent this type of material from wide application in structural concrete. The research and development of techniques which can minimize the adverse effect of RA on the concrete properties are highly requested. A specific mixing approach can also be helpful; here, mineral additives play a significant role for improvement of RA performance within the mixing process. However, delivery process can influence the homogeneity and uniformity of the concrete mixtures, resulting in negative effect on technical parameters. In this study, the impact of delivery time (0 min, 45 min, and 90 min) on the set of hardened concrete properties is presented while the three-stage mixing is used. Two kinds of additives—fly ash (FA) and recycled concrete powder (RCP)—were tested to coat the coarse fraction of recycled concrete aggregate (RCA) in the first step of mixing. For comparison, cement as coating material and natural aggregate instead the RCA were also used. The following parameters were tested after 28 days of setting and hardening: density, compressive strength, splitting tensile strength, water absorption capacity, and depth of penetration of water under pressure. Generally, 90 min of working with concrete mixtures left no significantly negative influence on tested characteristics. Based on ANOVA results, with prolonged discharge time, the changes in composition of the mixtures become less important for compressive strength, density, and water absorption

Verification of specific grinding parameters and strength activity index of glass and clay brick

The aim of this paper is to verify activity index (pozzolanic reactivity) of finegrained waste glass and clay brick. First part of this work consists from milling process with variation in milling parameters (time, grinding ratio) and determination (analysis) of the grain size distribution. Subsequently strength activity index is assessed for samples of particles size 50-60 μm. According to EN 450-1 method, tested samples does not reached an appropriate limit values as 25% substitute of cement. This result does not disqualify this type of construction and demolition waste as active additive in building materials but it is necessary improving their input parameters

Determination of The Basic Characteristics of Sludge for Utilization in Building Cement Composites

This paper presents the results of basic research using sludge as a secondary material produced during the process of wet aggregates grading. The basic objective of this study was to identify important properties of sludge for the further use as substitute filler in the cement composites. Results of tests executed, like determination of particle size, bulk density, chemical composition (XRF method), mineralogical composition (XRD method) and both clay lumps and humus content were compared with those of natural aggregate (reference sample), as well as with standard criteria. For all tested properties, sludge shows satisfactory parameters, except the granularity. Here samples demonstrate high portions of fine particles in the 0/4 range. Thus can be concluded, sludge has a potential to be used as filler in cement composites requiring bigger amounts of fine particles, like self-compacting concretes

Testing the Supplementary Cementitious Material Based on GGBFS and Zeolite for Prediction of the Activity Index

The article deals with cement supplementary materials based on ground granulated blast furnace slag and zeolite. Purpose of the experiment was to observe dependences (if they exist) between selected parameters (modulus of basicity, modulus of hydraulicity and initial setting time) and activity indexes, for easier and quicker way to determine or predict the activity index. Testing showed that moderate dependences between those parameters and activity indexes were observed. Results showed that prediction of activity indexes based on chemical composition is feasible

Effect of Aggregate Size on Recycled Aggregate Concrete under Equivalent Mortar Volume Mix Design

In this paper, the effect of the original aggregate size of the recycled aggregate on the mechanical properties of the recycled aggregate concrete was evaluated. A series of concretes were produced in which natural aggregates, recycled aggregates, and original aggregates in recycled aggregates were matched for a single particle size distribution curve. The replacement levels of recycled aggregate were 25% and 50%, and equivalent mortar volume mix design was applied for recycled aggregate concrete. The results show that the mechanical strength of recycled aggregate concrete increases with increasing original aggregate size. This effect was observed to be greater in concrete using recycled aggregate with a high residual mortar content