Tereza Pavlů

The Properties of Fine-Aggregate Concrete with Recycled Cement Powder

The main aim of this contribution is verification of properties of concrete with partial replacement of cement by recycled cement powder originating from waste concrete. The main topic of this article is the study of influence of partial replacement of cement by recycled cement powder (RCP) to the cement paste properties, workability of fresh concrete and strength development and dynamic modulus of elasticity of fine aggregate concrete with partial replacement of cement. The workability of fresh concrete were tested by flow table test. The compressive strength, tensile strength in bending and dynamic modulus of elasticity were tested at the age 7, 14, 28 and 90 days. Partial replacement of cement was 0, 5, 10 and 15 % for all these tests. Mechanical properties were investigated by using cubic and prismatic specimens. The determination of the initial setting time of cement paste were measured by automatic Vicat apparatus for replacement rate of cement 0, 5, 10, 15 and 25 %.

Behavior of Concrete Containing of Fine Recycled Aggregate

The use of coarse recycled aggregate in concrete is already accepted in the Czech Republic but with specific restrictions. The problem is the use of fine recycled aggregate (FRA) in concrete. This paper is focused on behavior of concrete containing FRA. FRA, which originated from recycling plant in the Czech Republic, was used in an experimental part. FRA was obtained from demolished and crushed concrete structures. Four concrete mixtures were designed and prepared. The first concrete mixture was reference which did not include FRA. Natural sand was replaced by FRA in other concrete mixtures in varying ratio. There were tested physical, mechanical and deformation properties of concrete. According to test results it is possible to say that the use FRA as partial replacement of natural sand in concrete mixtures.

Study Replacement of Cement with Recycled Cement Powder and the Environmental Assessment

This investigation is focused on possibility of partial cement replacement in concrete mixture and its environmental assessment. The cement in concrete mixture is replaced by recycled cement powder from modified construction and demolition (C&D) waste. Recycled cement powder were prepared in laboratory from C&D waste of high quality road concrete. The main goal of this investigation is optimize amount of recycled cement powder used as partial replacement of cement in concrete mixture according to mechanical, deformation and physical properties of concrete and environmental impact. The properties of the fine-aggregate concrete with partial replacement of cement by recycled cement powder were tested for this verification. The life cycle analysis was calculated for this optimization. The properties and environmental assessment of the fine-aggregate concrete with partial replacement of fine aggregate by fine recycled aggregate were examined for comparison.

Non-Destructive Testing of Concrete with Fine Recycled Aggregate

This paper is focused on non-destructive testing of concrete containing fine recycled aggregate (FRA). FRA was obtained from demolished concrete structures and crushed in the laboratory on fraction 0 – 4 mm. There were prepared four concrete mixtures. The first concrete mixture was control, did not include FRA. In other mixtures was natural replaced natural sand by FRA. There were tested workability of fresh concrete mixture and physical properties of hardened concrete. Finally, it is possible to say that the use of FRA influences the physical properties of concrete. The physical properties of concrete are connected with the durability of concrete. Therefore, it is necessary to focus on durability testing of FRA concrete in further research.

Efficiency Evaluation of Concrete Surface Treatment

This paper presents the simplified method of efficiency evaluation of surface protection products for concrete elements. This evaluation method was designed to consist of as few testing procedures as possible and to use as few specimens as well. Several testing processes most of which were based on the European technical standards were used to compare five commercially available products. Those comparisons served to assess whether the chosen method has sufficient informative value and does not require a disproportionate amount of time and money. The main examined properties were impact on color and reflectivity of the original surface, durability of the coating in extreme weather conditions, wettability of the surface and amount of labor needed for its maintenance. All of these experiments were optimized so that they could be performed on one type of specimen.

The Possibilities of the Utilization of Waste Glass as Partial Replacement of Fine Aggregate for HPC

This contribution is to verify the utilization of waste glass as partial replacement of fine aggregate for high performance concrete (HPC). Test results of fresh and hardened HPC will be presented. This study has been conducted through basic experimental research in order to analyze the possibilities of recycling waste glasses (grinding glass, milled glass powder from municipal waste) as partial replacement of silica powder for HPC.

Segregation of Steel Fibres of UHPFRC

The mixture of ultra-high performance concrete is often supplemented by steel fibres which can significantly improve the fracture energy of the concrete. The incorporation of steel fibres results in especially a significant increase of tensile strength and minimize the risk of brittle failure. However, these positive properties can be fully realised only if the fibres are uniformly distributed. Otherwise, that leads to different quality of the concrete and to deterioration of strength characteristics. The subject of this article is the segregation of steel fibres which is one of the frequent problems of poor distribution of fibres. The degree of segregation has been investigated depending on amount of fibre dosage, size of maximum aggregate size and degree of consistency of fresh concrete. Two types of steel fibres with circular cross-section of a diameter of 0.4 mm but with different lengths (12.5 and 25 mm) were used for experiments. The segregation was evaluated by the drop of the fibres on the cutting surface of specimens. The results showed that segregation was the most affected by the consistency of fresh concrete. The amount of fibre dosage as well as the size of maximum aggregate size did not significantly affect segregation.

The Properties of Fine Recycled Aggregate Concrete Containing Recycled Bricks from Construction and Demolition Waste

This paper presents research results of recycled fine aggregate concrete testing. The main aim of this contribution is verification of properties of fine aggregate concrete with partial replacement of fine natural aggregate by recycled masonry aggregate originated from construction and demolition waste. The influence of partial replacement of natural sand to mechanical properties and freeze-thaw resistance is described. The compressive strength and flexural strength were tested at the age of 28 and 60 days and after 25, 50, 75 and 100 freeze-thaw cycles. Partial replacement of natural sand was 0, 25 and 50 % for all these tests. Prismatic specimens were examined.

The Comparison of Properties of Fine Recycled Aggregate Concrete from Different Sources of Recycled Aggregate

The main aim of this contribution is comparison the properties of fine aggregate concrete with partial replacement of sand by fine recycled aggregate. The fine recycled aggregate originated from two different sources. The main topic of this article is the study of influence of the origin of FRA to fine aggregate concrete properties. The compressive strength, flexural strength and freeze-thaw resistance were tested. The mechanical properties and weight were examined after 28 and 60 days and after 25, 50, 75 and 100 cycles of freeze-thaw. Partial replacement of sand was 25 and 50 % for all these tests. The properties were investigated by using prismatic specimens.

The Carbonation Depth of Fine Recycled Aggregate Concrete

This paper is focused on carbonation resistance of fine recycled aggregate (FRA) concrete. Durability of FRA concrete is connected with uncertainties and doubts. One of the most unknown aspects of FRA cocnrete is carbonation resistance. This paper presents results of carbonation depth of FRA concrete. The FRA was originated from crushed construction and demolition (C&D) waste. There were prepared a total four concrete mixture. The first mixture was reference, did not include the FRA. In other concrete mixtures, natural sand was replaced by the FRA in various replacement ratios, specifically 10%, 20% and 30%. All prepared concrete mixtures were designated with the same parameters for clear comparison. From the test results it is possible to say that the use of the FRA as partial replacement of natural sand in concrete influences carbonation resistance of concrete. The carbonation depth was higher for concrete samples with the use of FRA. However it is possible to say that according to the carbonation resistance, the FRA concrete is possible to be used in the same applications as conventional concrete but it is necessary to verify this results.