Impact of the curing conditions and carbon dioxide ingress on heavyweight concrete

The present work investigates the influence of curing conditions on the mechanical and physical properties of heavyweight concrete. The prismatic bars of 40 mm × 40 mm × 160 mm dimension were cured in a climatic chamber (relative humidity 30%, average temperature 26°C), wet (100% of humidity, average room temperature 26°C) and CO2 chamber-wet (relative humidity 90%, average temperature 50°C and average CO2 concentration 20 %) conditions for 2, 7, 28 and 90 days. Density, compressive strength, dynamic modulus of elasticity, and longitudinal shrinkage were determined at different ages of curing. Mercury Intrusion Porosimetry was used to analyze and determine the influence of carbonation on pore structure evolution. Samples cured under CO2-wet conditions showed a higher compressive strength (54.05, 66.83, 84.98, 96.35 MPa) compared to that of the samples exposed to wet (45.49, 65.87, 78.91, 93.80 MPa) and dry (39.62, 46.52, 48.45, 45.28 MPa) conditions at all ages. The dynamic modulus of elasticity of CO2-wet cured samples (53.02, 51.48, 59.24, 67.60 GPa) was lower than that of samples cured in wet conditions (59.82, 66.76, 78.84, 80.27, GPa), but higher than that of dry-cured samples (45.74, 45.73, 43.91, 44.62 GPa). The density of the samples exposed to all curing conditions was higher than 3800 kg/m3. Carbonation led to a decrease in total porosity (from 10% to 20%) and an increase in density (from 320 to 390 kg/m3). Also, the time and curing conditions have strongly influenced the pore structure. The precipitation of calcium carbonate in the matrix of concrete and the acceleration of hydration reaction under wet conditions has led to a decrease in porosity.

Experimental Study of Selected Properties of Heavyweight Concrete Based on Analysis of Chemical Composition and Radioactive Elements of its Components

Heavyweight concrete is mostly used for its shielding properties in the nuclear power plants. These properties can already be influenced by the selection of the input materials. In the present study, concrete samples comprised of four-component binders based on CEM I 42.5 R, blast furnace slag, metakaolin and limestone and a mixture of barite and magnetite aggregate, were investigated. Based on Energy Dispersive X-ray Fluorescence, Neutron Activation, and Prompt-Gamma Activation analyses, three concrete designs were prepared and tested. Mechanical, physical (namely cubic compressive strength, bulk density, longitudinal deformation, and dynamic modulus of elasticity) and thermal properties (thermal conductivity coefficient, specific heat capacity, and thermal diffusivity), which should be influenced by the long-term exposure to irradiation were investigated. Presented results confirmed that the prepared samples are heavyweight concrete with bulk density higher than 3400 kg.m-3 with a low level of longitudinal deformation (between 0.265 ‰ and 0.352 ‰). All the prepared samples belong to the C 35/45 concrete strength class.

Estimation of the Probability of Cracking of Facade Coatings

Information on the stress state of protective and decorative coatings during the curing process, in particular on the cohesive state of destruction, is given. The influence of the type of substrate on the change in internal stresses in the coating is considered. It was revealed that the greatest value of shear stresses is observed in coatings on a heavyweight concrete substrate. The subsequent increase in temperature after curing to 50°C leads to an increase in the value of the normal stresses. The probability of cracking of coatings during thermal aging is estimated. It was revealed that during aging there is an exponential decrease in the cohesive strength of coatings and an increase in internal stresses. Aging tends to increase the likelihood of cracking of coatings. The change in stresses in coatings as a result of seasonal fluctuations in air temperature is considered.

Formwork Pressure of a Heavyweight Self-Compacting Concrete Mix

High-fluidity and self-compacting concrete (SCC) mixes were developed using special aggregates for radiation-shielding concrete. The special aggregates comprised heavyweight and hydrous aggregates (crushed magnetite, crushed serpentine, and their mixtures), which were selected to provide an enhanced attenuation of gamma and neutron radiation, respectively. For the mixed concrete design with a bulk density of up to 3570 kg/m3, two cement types were used: Portland cement CEM I and slag cement CEM III/A. The basic properties of the fresh self-compacting concrete were evaluated and the lateral formwork pressure exerted by the freshly mixed self-compacting concrete was measured and analyzed. An original test setup was developed for the determination of the lateral pressure on the square column formwork with pressure measurements carried out using six strain gauge pressure transducers, which was adequate for heavyweight concrete mixture testing. Self-compacting concrete mixtures containing a magnetite aggregate or blends of serpentine and magnetite aggregates with a slump flow of at least 550 mm were developed. The lateral pressure on the formwork was directly proportional to the density of the self-compacting heavyweight concrete mixes. The maximum values of the lateral pressure recorded in the test at a casting speed of 1.5 m/h did not exceed 27 kPa and 55% of hydrostatic pressure. Concrete mixtures with basalt, magnetite, and magnetite/serpentine blended aggregates were found to develop sufficient shear strength for proper stability during casting.

Technological and organizational problems in the construction of the radiation shielding concrete and suggestions to solve: A case study

Protection of buildings against the pernicious radiation types can be achieved by simultaneous structural and shielding parameters. Those shields are mainly made of heavyweight concrete, which causes many serious problems in the areas of technology, supply logistics, financial supply, Occupational Safety & Health Administration, and substitutions of structural and material solutions. This work presents a case study of the construction of the university building with rooms requiring protection against malicious radiations. Apart from that, it presents the problems and solutions that occurred during the construction from the perspective of the works contractor. This study was also expanded to include the analysis of alternatives for construction-materials. The obtained results were used to develop a generalized scheme, which will be helpful in the preparation and implementation of any facilities requiring fixed radiation shields.

Effect of nano-silica slurry on engineering, X-ray, and γ-ray attenuation characteristics of steel slag high-strength heavyweight concrete

High molar mass materials (nano-silica slurry [NSS] and aggregate of steel furnace slag [ASFS]) can improve concrete shielding properties. However, only a few studies have been reported in this regard. Hence, this paper aims to determine the effect of NSS and ASFS on the properties of the resulting steel slag heavyweight concrete (SSHWC). The use of NSS in this study is a novel contribution. Furthermore, the maximum percentage of NSS to be introduced into the concrete for maximum effect was also optimized. This study also implemented an investigation program with six concrete mixtures prepared using ASFS as the primary by-product aggregate. The engineering, X-ray, and γ-ray attenuation characteristics of the SSHWC were evaluated. The results showed that the addition of NSS in SSHWC at the optimal content of 3% by weight of cement improved the X-ray shielding by 6.4%. Besides, all the concrete’s engineering and γ-rays’ properties were enhanced correspondingly.