Beton cu pulberi reactive armate cu fibre din oţel

Ultra High Strength and Performance Concrete development is a relatively new industry. The last 150 years have shown that despite of a constant increasing resistance for the concrete, the practical applications were often behind to these innovations in materials science. This appears to be due to increased costs as the resistance increases per unit volume and a caution restraint to use new materials in practical applications. This paper is intended to be as an encouragement to present a practical structural applications of Ultra High Performance Concrete (BUIP) or reactive powder concrete (BPR), first developed in Romania, by using locally available materials, including waste reusing and thereby making an ecological green concrete. This concrete has a viscous consistency but a slump flow similar to the self compacting concrete (SCC), and compressive strength values exceed 150 MPa (150 ÷ 200 MPa)

Eco-efficient cementitious composites with large amounts of waste glass and plastic

This paper presents an experimental study, which has been lacking to date, into the properties and applications of Waste Glass-Plastic Cementitious (WGPC) composites incorporating recycled aggregates as a full replacement of natural aggregates, with direct application in highly eco-efficient construction components. Detailed experimental assessments on the fresh properties, strength, and durability characteristics of such composites are undertaken. Particular focus is given to the mix rationale and optimisation process as well as possible routes of exploitation of such materials in construction elements. Experimental assessments showed that such composite materials meet the strength and durability criteria for direct application in practice. The best balance in terms of strength and workability was achieved for a waste glass-to-plastic aggregate ratio of 92/8. The presence of relatively large amounts of recycled waste glass particles with small sizes acted as secondary hydration products and contributed to achieving an adequate strength of the material. Besides lower unit weight and superior thermal properties compared to conventional concrete, WGPC components have shown a reliable behaviour under vehicle impact loading and potential wider application in sustainable non-structural construction applications

Achieving Mixtures of Ultra-High Performance Concrete

Ultra-High Performance Concrete (UHPC) is a relatively new concrete. According to [11] UHPC is that concrete which features compressive strength over C100/115 class. Up to this point standards for this type of concrete were not adopted, although its characteristic strength exceeds those specified in [33]. Its main property is high compressive strength. This provides the possibility of reducing the section of elements (beams or columns) made of this type of concrete, while the load capacity remains high. The study consists in blending mixtures of UHPC made of varying proportions of materials. The authors have obtained strengths of up to 160 MPa. The materials used are: Portland cement, silica fume, quartz powder, steel fibers, superplasticiser, sand and crushed aggregate for concrete - andesite

Disperse reinforced concrete used in obtaining prefabricated elements for roads

Concrete is the most used material in construction. By improving the performance of materials and of technologies, concretes with outstanding performances were also developed, in the past two decades. Concrete with dispersed reinforcement represents a new generation of reinforced concrete that combines a good behavior of concrete compressive strength with an increased tensile strength of steel fibers. Using this material, monolithic and prefabricated concrete elements with high mechanical strengths and high durability can be obtained. Technological processes for preparation of concrete with dispersed reinforcement are similar to the conventional methods and do not involve using additional equipment for dosing the dispersed reinforcement. The study aimed the development of road plates made with optimized disperse- reinforced concrete. The first tests were done on plates from the gutter roadway, having a classic reinforcement, using different percentages of fibre reinforcement in the concrete composition, leading to the development of a new optimized economical solution. The results prove the enhanced characteristics of the disperse-reinforced concrete versus conventional concrete, and hence of the developed concrete plates

Modelling of the bending behaviour of double floor systems for different contact surfaces

In the practice of prefabricated concrete structures considerable surfaces of intermediate floors are constructed using double floor systems with prefabricated bottom layer and upper layer. This second layer is cast on site. The quality of the prefabricated concrete is often of superior class with respect to the monolithic layer. In the service state of the double floor system, important compressive stresses appear in the upper concrete layer. On the other hand, the bond quality between the concrete layers cast in successive stages raises questions especially in the case of hollow core floor units with no connecting reinforcement in-between. The paper presents results of the numerical models prepared for double floor elements having different thicknesses for the top and bottom layers, subjected to bending. Three situations have been studied: stepped top surface of the prefabricated slab with no connecting reinforcement, broom swept tracks on the prefabricated slab with no connecting reinforcement and broom swept tracks on the prefabricated slab with stirrups connecting the concrete layers. For each situation two different ratios of the thicknesses of the layers have been considered. The results are emphasizing the critical regions of the elements, the differences in crack development and in the behaviour resulting from surface preparation and use of connecting reinforcements

Study on the Durability of Road Concrete with Blast Furnace Slag Affected by the Corrosion Initiated by Chloride

In order to assess the resistance of the road concrete to the penetration of the chloride ions, we used the rapid test RCPT in compliance with ASTM C1202. But, in order to increase the reliability of the rapid test of assessing the resistance of chloride ions’ permeability through measurements of the electrical conductivity, after finishing the RCPT test, we have also measured the depth of the chloride front migrating in the concrete. Road concrete mixtures were prepared in which blast furnace slag (GGBS) was incorporated as a binder and blast furnace slag (ABS) as crushed slag aggregate to the size of 0/4 mm. The effect of the blast furnace slag on the RCPT results was investigated and correlated with porosity trends, carbonatation layer depth, and with the compression strength values, by comparison with the level of results obtained on concrete mixtures made with conventional materials. The measurement of the migrated chlorine front in the concrete together with the determined physical and mechanical characteristics confirms the efficiency of the blast furnace slag incorporated in the concrete and supports the reliability of the rapid penetration test of chlorine ions RCPT using the procedure from ASTM C 1202

Freeze–Thaw Effect on Road Concrete Containing Blast Furnace Slag: NMR Relaxometry Investigations

The present work investigates the effect of freeze–thaw cycles on the porosity of three mixtures of road concrete containing blast furnace slag in comparison with two mixtures made with conventional materials. The main technique used in our investigations is nuclear magnetic resonance (NMR) relaxometry. This permitted the extraction of information with respect to the freeze–thaw effect on pore-size distribution, which influences both the mechanical strength and the molecular transport through the material. Moreover, by using this technique, the structure of the air voids was analyzed for the entire pore system in the cement paste and the aggregate particles. The samples under study were first dried in a vacuum oven and then saturated with water or cyclohexane where the distribution of the transverse relaxation times of the protons was recorded. The NMR relaxation measurements were performed on samples extracted from specimens maintained at 300 freeze–thaw cycles and on control samples extracted from specimens kept in water during the freeze–thaw period. Scanning Electron Microscopy (SEM) was used to analyze the microstructure of concrete samples in order to obtain information about the pore sizes and the distance between them. The results from the NMR relaxation measurements were consistent with those obtained by using standard techniques for determining the porosity and the freeze–thaw resistances. The investigations made it possible to establish the optimal composition of blast furnace slag that can be incorporated into road concrete compositions. This non-invasive technique can also complete standard techniques for assessing the porosity and the progress of internal cracks during the freeze–thaw test

Revealing the Influence of Microparticles on Geopolymers’ Synthesis and Porosity

Geopolymers are zeolites like structures based on hydrated aluminosilicates units of SiO4 and AlO4. These units, known as poly(sialate), poly(sialate)-siloxo or poly(sialate)-disiloxo are chemically balanced by the group I cations of K+, Li+, or Na+. Simultaneously, the chemical reaction of formation, known as geopolymerization, governs the orientation of the unit, generating mesoporous structures. Multiple methods can be used for pore structure and porosity characterization. Among them, nuclear magnetic resonance (NMR) relaxometry allows the detection of the porous structure in a completely nonperturbative manner. NMR relaxometry may be used to monitor the relaxation of protons belonging to the liquid molecules confined inside the porous structure and, thus, to get access to the pore size distribution. This monitoring can take place even during the polymerization process. The present study implements transverse relaxation measurements to monitor the influence introduced by the curing time on the residual liquid phase of geopolymers prepared with two different types of reinforcing particles. According to our results, the obtained geopolymers contain three types of pores formed by the arrangement of the OH− and Si groups (Si-OH), Si-O-Si groups, Si-O-Al groups, and Si-O rings. After 48 days, the samples cured for 8 h show a high percentage of all three types of pores, however, by increasing the curing time and the percentage of reinforcing particle, the percent of pores decrease, especially, the gel pores