Protection Of Concrete Structures Research Articles

INFLUENCE OF THE AGE OF EPOXY DISPERSION ON THE EFFECTIVENESS OF PROTECTION OF CONCRETE SURFACES

The scope of this paper is to test stability and mechanical and chemical properties of a modern freshly mixed epoxy dispersion, and as a variant, of a dispersion which is two years old. During ageing, the dispersion particles probably agglomerate, which is tested by laser diffraction and by sedimentation in a cylinder. Physical-mechanical tests assess the appearance, drying speed and mechanical properties of the film. Chemical tests focus on assessing the resistance of films of dispersions of different ages to common chemicals and to chemical defrosting agents. It is possible to say that two years of dispersion storage lead to a considerable increase in the diameter of a certain number of dispersion particles with the subsequent effect of increasing the sedimentation speed. The hardened film of a two-year old dispersion dries faster, has a rougher surface, is softer, but on the other hand, is less elastic and its adhesive capacity to the substrate is worse. Its chemical resistance is decreased but its defrosting agent resistance remains good. Due to the two-year storage of the epoxy dispersion, most of the monitored parameters decrease, nevertheless, certain protection of concrete structures by a hardened film of such epoxy dispersions is possible.

Inhibiting Sulphate Attack on Concrete by Hydrophobic Green Plant Extract

Organic base (Amine) and inorganic base (Nitrite) have been known for protection of concrete structures but are not commercially indigenous to most developing economies due to manufacturing difficulties and are toxic to the environment. Also inhibitors are not known to stop sulphate attack in concrete. Hence, the objective of the present investigation was to study a novel, eco-friendly and hydrophobic green plant extracts inhibitor and compares its effectiveness with established calcium nitrite and ethanolamine inhibitors. Bambusa Arundinacea (Green plant extracts), calcium nitrite and ethanolamine corrosion inhibitors were selected for the present investigation. Compressive strength of 100×100×100mm concrete cubes after 7, 28 and 90 days of curing test was used. The results of the inhibitors studied showed that Bambusa Arundinacea has superior compressive strength compared to calcium nitrite and ethanolamine. Bambusa Arundinacea may be considered a better substitute for nitrite and amine- based corrosion inhibiting admixtures for durable concrete structures due its pore blocking effects.

Modelling of concrete perforation

The analysis of penetration of warheads in concrete protective structures is an important part of the study of weapon effects on protective structures. This type of analysis requires that the design load in the form of a warhead is determined, and its characteristic and performance within a protective structure is known. Constitutive equations for concrete subjected to weapon effects have been a major area of interest for a long time, and several material models for concrete behaviour are developed. However, it is not until recent years that it has been possible to use finite element (FE) analyses to simulate the behaviour of concrete targets during projectile penetration with acceptable results. The reason for this is a combination of several factors, e.g. development of suitable material models for concrete, enhancement of numerical methodology and affordable high capacity computer systems. Furthermore, warhead penetration has primary been of interest for the armed forces and military industry, with a large part of the conducted research being classified during considerable time. The theoretical bases for concrete material behaviour and modelling with respect to FE analyses of projectile penetration are treated in the thesis. The development of weapons and fortifications are briefly discussed in the thesis. Warheads may be delivered onto a protective structure by several means, e.g. artillery, missiles or aerial bombing, and two typical warhead types were used within the study. These warhead types were artillery shells and unitary penetration bombs for the use against hardened targets, with penetration data for the later warhead type almost non-existing in the literature. The penetration of warheads in concrete protective structures was therefore studied through a combination of experimental work, empirical penetration modelling and FE analyses to enhance the understanding of the penetration phenomenon. The experimental data was used for evaluation of empirical equations for concrete penetration and FE analyses of concrete penetration, and the use of these methods to predict warhead penetration in protective structures are discussed within the thesis. The use of high performance concrete increased the penetration resistance of concrete targets, and the formation of front and back face craters were prevented with the use of heavily reinforced normal strength concrete (NSC) for the targets. In addition, the penetration depths were reduced in the heavily reinforced NSC. The evaluated existing empirical penetration models did not predict the behaviour of the model scaled hardened buried target penetrators in concrete structures with acceptable accuracy. One of the empirical penetration models was modified to better describe the performance of these penetrators in concrete protective structures. The FE analyses of NSC gave reasonable results for all simulation cases, with the best results obtained for normal impact conditions of the penetrators.

Early stage beneficial effects of cathodic protection in concrete structures

AbstractOver the last 25 years, cathodic protection (CP) of reinforced concrete structures suffering from chloride induced reinforcement corrosion has shown to be successful and durable. CP current causes steel polarisation, electrochemical reactions and ion transport in the concrete. CP systems are designed based on experience, which results in conservative designs and their performance is a matter of wait‐and‐see. CP systems can be designed for critical aspects and made more economical using numerical models for current and polarisation distribution. Previously, principles of numerical calculations for design of CP systems were reported. The results were satisfactory, except in terms of current density for active corroding systems. This was suggested to be due to neglecting beneficial effects of CP current flow. One of the beneficial effects is pH increase at the steel surface due to oxygen reduction. As the pH increases, the corrosion rate decreases and the current demand decreases. A simple model was set up for this transient process, suggesting that such effects should occur on the time scale of hours to days. This model was validated from start up data of a CP field trial system on part of a bridge. Field results confirmed the modelling proposed here.

Cathodic protection of concrete structures containing calcareous aggregates in tropical‐humid marine environments

PurposeTo evaluate the performance of two cathodic protection (CP) systems applied to steel reinforced concrete structures manufactured with calcareous aggregates and exposed to the tropical‐humid marine environment at the Yucatán peninsula in Mexico.Design/methodology/approachRectangular concrete beams were manufactured using a water/cement ratio = 0.65, with and without the addition of NaCl in the mixing water. Specimens subjected to CP, eight to impressed current cathodic protection (ICCP) and eight to sacrificial anode cathodic protection (SACP) were partially immersed in natural seawater during 360 days. The half cell potential (HCP) and the current consumption were recorded during the total exposure time.FindingsThe measured HCP values of the steel rebar in the beams subjected to SACP did not attain protection potential levels. However, the galvanic couple Zn‐steel provided enough current for the protection of the steel. Visual inspection of concrete cores extracted from the beams indicated that corrosion products were not present at the steel‐concrete boundary. On the other hand, the ICCP applied to eight concrete beams provided excellent corrosion protection to the steel rebar.Originality/valueThis work revealed that the SACP system (thermally sprayed zinc) works well in high relative humidity environments and can be successfully used to protect steel reinforced concrete structures manufactured with calcareous aggregates which are endemic of the region and commonly used for infrastructure construction in the Yucatán peninsula.

Effect of plasticizers on structure and mechanical properties of Thiokol sealant

The compatibility of the Thiokol sealant U-30M with plasticizers of different types was estimated. The rheological properties of the plasticized compositions and the effect of the nature and concentration of plasticizer on the properties of vulcanizates were studied. It is shown that the addition of chlorinated paraffins (KhP-52 and KhP-470), a flotation agent, and PL-105 as plasticizers considerably improves the dielectric properties of the sealant. The formulations of coatings designed for the protection of concrete structures from corrosive media and for the manufacture of roofing and waterproofing materials were developed.

Establishing performance criteria for concrete protective structures

Based on an evaluation of hazard scenarios and past industrial accidents, the required performance of concrete protective structures was studied. The importance of consistency and completeness of hazard scenarios is emphasised. Consistency considerations are illustrated in more detail in a discussion on tightness criteria for concrete protective structures.

Establishing performance criteria for concrete protective structures

Based on an evaluation of hazard scenarios and past industrial accidents, the required performance of concrete protective structures was studied. The importance of consistency and completeness of hazard scenarios is emphasised. Consistency considerations are illustrated in more detail in a discussion on tightness criteria for concrete protective structures.

5531873 Electrode arrangement to be used in the cathodic protection of concrete structures and a fixing element

5531873 Electrode arrangement to be used in the cathodic protection of concrete structures and a fixing element

Repair and protection of concrete structures

Repair and protection of concrete structures