HIGH STRENGTH CONCRETES BASED ON THE CHOICE OF THE BEST PARTICLE SIZE DISTRIBUTION IN AGGREGATE

The requirements of the modern (high-end) construction industry demand the development of new types of concrete of high, and especially very high strength and with significantly improved properties in terms of durability. They provide new possibilities in the field of concrete technology of high strength and performance. When designing the composition of high-strength concrete (HSC), a special attention should be paid to the particle size distribution of aggregates, which should be chosen so as to achieve an "optimal" packing of the aggregate grains. The maximum grain size has been reduced to 2 mm. The Funk-Dinger formula was used to calculate the particle size distribution, which also takes into account fine particles of mineral powder additives. CEM I 52.5R, pure quartz sand, quartz filler, silica fume, powerful superplasticizer and low water/binder ratio were chosen for making HSC. In total, five different concrete mixtures were made. The paper presents the results of testing important properties of hardened concrete at ages from 1 day to 90 days and statistical processing of the obtained test results

PROPERTIES OF STEEL-POLYPROPILENE HYBRID FIBERS REINFORCED CONCRETE

This paper present the results of mechanical properties of hybrid reinforced concrete made by adding polypropylene and steel fibers into concrete mixture. For the testing purposes were used steel fibers with hooked ends and monofilament polypropylene fibers. The total of 5 batches of concrete were made: concrete with addition of steel fibers, polypropylene fibers and their combination in amount of 0,5 % of the concrete volume. The test results show that concretes made by adding of 0.4% steel and 0.1% polypropylene fibers have better performance compared to other concretes

Properties of Self-compacting Concrete Produced with Biomass Wood Ash

The demand of the contemporary society for renewable energy sources lead to the increase of the bio-power plants. Accordingly, the amount of ash generated by burning the biomass is increased, and its disposal becomes a large environmental problem. The paper presents the research of potential use of biomass wood ash as a partial replacement for coal fly ash (10%, 20%, 30% and 40% of mass) in production of self-compacting concrete (SCC). The effects of biomass wood ash on the properties of SCC in fresh and hardened states have been examined, as well as on the properties of durability. Test results indicated that the biomass wood ash slightly reduces the flowability and passing ability of SCC, while its addition enhances the viscosity of SCC and significantly prevents segregation and bleeding. SCCs with the contents of biomass wood ash up to 20% have approximately same mechanical strength as the reference mixture. Biomass wood ash has no negative effect on the resistance of concrete to the action of water under pressure, but a decrease of freeze/thaw resistance with de-icing salt is detected as its contents increases. The addition of biomass wood ash into SCC increases the drying shrinkage in the initial period of drying (up to 14 days), and it is decreased in a later phase

Impact of crushed mineral aggregate on the pumpability of concrete during transport and placement

In the spirit of the sustainable buildings, and with the goal of protection of river courses, in the near future an already announced directive ordering closing down of a large number of river aggregate dredging operations will be adopted. For that reason, usage of crushed mineral aggregate in concrete mixes is increasing. Irrespective of downsides of the fined crushed mineral aggregate, such as the presence of fine particles bordering the upper permissible limit and the unfavorable shape of the grain of the course aggregate for obtaining liquid consistency required for the pumpable concrete, the demanded pumpability of concrete during transport and placement has been achieved. By adding admixtures to concrete, the required concrete properties, such as: frost resistance, simultaneous frost and salt resistance and water tightness have been achieved

Gaussian Regression Process for Prediction of Compressive Strength of Thermally Activated Geopolymer Mortars

The primary objective of this research is the development of a prediction model of the compressive strength of geopolymer mortars made with fly ash and granular slag which hardened in different curing conditions. Data for the numerical analysis were obtained by experimental research; for this purpose 45 series of geopolymer mortars were made, 9 of which were cured in ambient conditions at a temperature of 22 °С, and the remaining were exposed to thermal activation for a duration of 24 h at the temperatures of 65 °С, 75 °С, 85 °С and 95 °С. Using machine learning, a Gaussian regression method was developed in which the curing temperature and the percentage mass content of fly ash and granular slag were used as input parameters, and the compressive strength as the output. Based on the results of the developed model, it can be concluded that the Gaussian regression process can be used as a reliable regression method for predicting the compressive strength of geopolymer mortars based on fly ash and granular slag

Hydro-abrasive resistance and mechanical properties of rubberized concrete

U radu su prikazani rezultati ispitivanja hidroabrazivne otpornosti i mehaničkih svojstava betona s dodatkom gumenih granula. Sitni riječni agregat zamijenjen je s 10, 20 i 30 posto reciklirane granulirane gume (u odnosu na ukupan volumen). Rezultati ispitivanja pokazuju da zamjenom sitnog riječnog agregata granuliranom gumom dolazi do povećanja hidroabrazivne otpornosti betona do 10 posto. Zamjena sitnog riječnog agregata gumenim materijalom dovodi do povećanja sposobnost raspodijele energije i duktilnosti.Results obtained by testing hydro-abrasive resistance and mechanical properties of concrete with rubber granules are presented in the paper. Fine river aggregate is replaced with 10, 20, and 30 percent of recycled granulated rubber (with respect to the total volume). Research results demonstrate that replacement of fine river aggregate by granulated rubber increases hydro-abrasive resistance of concrete by up to 10 percent. The replacement of fine river aggregate by rubber increases the energy dissipation capacity and ductility

Characteristics of Mortar from fhe Archeolical Site Romuliana – Gamzigrad

Felix Romuliana is a palace erected during the rain and after the design of the Emperor Gaius Valerius Galerius Maximianus. It belongs to the category of monuments of Roman court architecture which is associated with the time of Tetrarchy. During the archeological excavations, two fortification systems were discovered, they younger outer system with twenty polygonal massive towers, and an older inner system with sixteen towers of quadragonal and octagonal towers flanking the gates. The younger outer fortification is polygonal. The communication east-west connecting two gates divides interior space into two entities. Systemic archeological research last since 1953 by probing the northwest part of the inner space. Conservation works run simultaneously with the excavations. Mortar samples were taken from the towers XI and XII of the old fortification, as well as from the tower 15 and the part of the rampart between towers 1 and 3 of the younger fortification. Mortars were analyzed with the goal of obtaining information about morphological, mineralogical, chemical and basic physical properties of mortar. For analysis of these properties, optical microscopy and scanning electronic microscope were used. Depending on the location sampled mortars, there are differences of individual properties of mortar. The optical examination of macroscopic appearance of mortar samples indicated that those are limestone binder mortars. Aggregae grains are both river and stone aggregate. Mortar porsity differs depending on the location where samples were taken

HYDRO-ABRASIVE RESISTANCE AND MECHANICAL PROPERTIES OF CONCRETE WITH ADDED FLY ASH

The durability of hydraulic engineering structures mostly depends on the resistance of their concrete surfaces to mechanical abrasion. In this paper, we study the hydro-abrasive resistance and mechanical properties of concrete in which cement is partially replaced with fly ash in various proportions. To evaluate these concretes, we measured their compressive strength, flexural strength, static modulus of elasticity, ultrasound velocity through concrete, and sclerometer rebound. The hydro-abrasive resistance of concrete with 15% fly ash was similar to that of reference concrete without fly ash. However, concretes with more than 15% fly ash exhibited lower resistance to abrasive erosion than the reference concrete. Also, the mechanical properties of the concrete deteriorated as the fly ash content increased