Investigation of the microstructure and carbonation of CS¯A-based concretes removed from service

The microstructure, mineralogy and depth of carbonation of two concrete samples, one removed from a normal strength crane column and the other from a high-strength pile, are reported. The normal strength CS¯A cement concrete had a high w/c ratio; microstructural images show that clinker tends to hydrate almost completely. But for high-strength CS¯A cement concretes, made with low w/c ratios, large amounts of partially hydrated clinker grains remain as a microaggregate.

CS¯A cements and concretes are subject to carbonation in service conditions. The usual method of determining depth of carbonation, the phenolphthalein test, does not work with aged CS¯A matrices. A new method, using infrared microscopy, has been used to determine carbonation depth of aging CS¯A cement concrete. It has been shown that carbonation of a normal strength CS¯A cement concrete exposed to open air for 16 years averages 0.5 mm/year, and is thus comparable with reported rates of carbonation of OPC concretes. The high-strength CS¯A concrete carbonated at a maximum rate of 60 μm/year.     

Effect of sodium monofluorophosphate treatment on microstructure and frost salt scaling durability of slag cement paste

Sodium-monofluorophosphate (Na-MFP) is currently in use as a surface applied corrosion inhibitor in the concrete industry. Its basic mechanism is to protect the passive layer of the reinforcement steel against disruption due to carbonation. Carbonation is known as the most detrimental environmental effect on blast furnace slag cement (BFSC) concrete with respect to frost salt scaling. In this paper the effect of Na-MFP on the microstructure and frost salt scaling resistance of carbonated BFSC paste is presented. The results of electron microscopy, mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD) are discussed. It is found that the treatment modifies the microstructure and improves the resistance of carbonated BFSC paste against frost salt attack.     

Internal frost resistance and salt frost scaling of self-compacting concrete

This article outlines laboratory and analytical studies of salt frost scaling and internal frost resistance of self-compacting concrete (SCC) that contains increased amount of filler, different air content, and dissimilar methods of casting. The results were compared with the corresponding properties of normal concrete (NC) with the same water-to-cement ratio (0.39) and air content (6%). The start of the testing was applied at ages of 28 and 90 days. The strength development of the concrete was followed in parallel. Six SCC and two NC were studied. The effects of normal and reversed order of mixing (filler last), increased amount of filler, fineness of filler, limestone powder, increased air content, and large hydrostatic concrete pressure were investigated. The results indicated a substantial improvement of the internal frost resistance of SCC as compared to NC. The salt frost scaling performed more or less in the same way in SCC and in NC. No relationship of frost resistance was found to the air-void structure of the concrete.     

Determining the moisture content of refractory concretes

Conclusions A portable apparatus was developed for measuring the moisture content of concrete at temperatures up to 200°C. The accuracy of the measurements is ±0.3 abs. %.The apparatus was tested on the main types of refractory concrete. Results were satisfactory.     

Strength properties of nylon- and polypropylene-fiber-reinforced concretes

The strength potential of nylon-fiber-reinforced concrete was investigated versus that of the polypropylene-fiber-reinforced concrete, at a fiber content of 0.6 kg/m³. The compressive and splitting tensile strengths and modulus of rupture (MOR) of the nylon fiber concrete improved by 6.3%, 6.7%, and 4.3%, respectively, over those of the polypropylene fiber concrete. On the impact resistance, the first-crack and failure strengths and the percentage increase in the postfirst-crack blows improved more for the nylon fiber concrete than for its polypropylene counterpart. In addition, the shrinkage crack reduction potential also improved more for the nylon-fiber-reinforced mortar. The above-listed improvements stemmed from the nylon fibers registering a higher tensile strength and possibly due to its better distribution in concrete.     

Abrasion resistance of refractory concretes and linings

Results are provided for determination of the abrasion resistance of refractory concretes of different composition according to the standard ASTM C-704. Principles are considered for constructing abrasion-resistant linings in order to protect heating units in various branches of industry. __________ Translated from Novye Ogneupory, No. 3, pp. 81–85, March, 2007.     

Abrasion resistance of refractory concretes

Conclusions With the use of abrasion resistant aggregate (corundum or corundum-mullite compositions) the highest abrasion resistance, approximating to that of fired dense chamotte articles) during heating to 1100C is possessed by concretes having a phosphate bond and containing water glass.Concretes based on high-alumina and aluminous cements around the critical temperatures have a low abrasion resistance, but at temperatures above 1100C as a result of the formation of a ceramic bond their abrasion resistance increases.Translated from Ogneupory, No. 4, pp. 41–47, April, 1967.     

Carbon resistance of corundum concretes

Conclusions The resistance of the corundum concretes to carbon during direct interaction under the conditions of high temperature isothermal holding is quite high. After holding for a period of 120 h at 1580°C, the weight loss of the concrete specimens is insignificant (0.2–0.4%) without exception.Modifying the structure of the concretes using chromium oxide and a mixture of lignosulfonates makes it possible to reduce the weight loss in the carbon-bearing medium.Translated from Ogneupory, No. 4, pp. 11–15, April, 1988.     

Structure evolution of corundum concretes

Conclusions Structure evolution of the corundum concretes based on the binders of different compositions was studied.We demonstrated the effect of Cr₂O₃, CCLS, and technological (technical-grade) lignosulfonate on the strength gain of the cement stone and the concrete based on it, the phase composition of the cement stone and the concrete, their variation during the process of heat treatment, and on the microstructure.The ability of these additives to increase the degree of hydration of the high-alumina cement was established. The formation of a large quantity of aluminum hydroxide and calcium hydromonocarboaluminate confirm this fact.The evolution of a dense and strong structure of the corundum concrete based on the high-alumina cement and the occurrence of additional growth during the high-temperature firing process due to the formation of CA₆ and the solid solutions of corundum and CA₆ with Cr₂O₃ were shown.Translated from Ogneupory, No. 4, pp. 7–14, April, 1989.     

Determination of the electrical conductivity of heat-resistant concretes

The problem of the electrical conductivity of heat-resistant concretes and bonding agents is considered and a method for determining this parameter is suggested. In addition to the thermal resistivity, the electric conductivity is a factor affecting the lifetime of lining materials for high-temperature devices. The problem is especially urgent in electric heaters. Translated from Ogneupory, No. 7, pp. 25–26, July, 1994.     

Assessment of the “rheoplasticity” of concretes

In the present paper it is proposed to evaluate the rheological behaviour and the plasticity of fresh concrete by means of the determination of a so-called “rheoplasticity” index defined as RPI = 1/∫ BdS or RPI′ = 1/B′, where B is the bleeding capacity, S is the slump, and B′ is the bleeding capacity of very flowable concrete (S = 20 cm). Since concretes with high value of RPI or RPI′ can be obtained only with relatively low water/cement ratio and by using certain highly fluidifying additives, the properties of these hardened concrete are in general very good.     

Preparation and properties of corundum HCBS and ceramic concretes. Part 3. Casting and volume constancy of ceramic concretes

Vibration casting and casting from a self-spreading mix with an original moisture content of molding systems of 3.8 – 4.2% are used to prepare coarse-grained (D _max = 10 mm) and medium-grained (D _max = 3 mm) corundum ceramic concretes with a corundum-mullite matrix system. Depending on the heat treatment temperature, the amount of their open porosity is 11 – 15%, and the ultimate strength in compression reaches 160 MPa. Both cast and compacted ceramic concretes have high volume constancy during heating or firing, and also in service. Linear shrinkage does not exceed 0.2 – 0.5%.     

Ceramic cements and ceramic concretes of quartz-chamotte composition

Conclusions On the basis of quartz sand and scrap chamotte refractories (28.0% Al₂O₃, 67.0% SiO₂) we obtained highly concentrated bonding suspensions (cement slips) of mixed composition enabling us to form castings with a porosity of 12.2–18.3% characterized by bending strengths of up to 4.5 MPa and compressive strengths of up to 32.4 MPa.During the use of quartz-chamotte suspensions as bond and of chamotte scrap (grog) as the filler we obtained ceramic concretes with an original compressive strength of 18.4–25.6 MPa, and a porosity of 14.6–19.2%.We studied the change in the physicomechanical properties of the bonds (cements) and the ceramic concretes during heat treatment in the range 100–1450°C.The chamotte ceramic concretes based on quartz-chamotte bonds of the optimal compositions possess an increased spalling resistance (16 water-heat cycles from 1300°C during testing of specimen cubes with edges of 50 mm).Translated from Ogneupory, No. 5, pp. 5–9, May, 1986     

Dynamic strength of polymer modified and fiber-reinforced concretes

For evaluating the performance of concrete construction such as foundation piles, a knowledge of the dynamic properties of concrete is also required. Some results of a study of concrete under dynamic impact loading are given in this paper. ø 100×200 mm cylindrical specimens were cast from plain and polymer cement concrete; some of the specimens were reinforced by polypropylene fibers also. The experimental details of the Hopkinson split-bar method used are described. The dynamic strength of concrete obtained was 40–45 % higher than the static strength. Compared to normal concrete, polymer cement concrete showed 30–35 % higher dynamic strength, and significantly higher energy transmission capacity.