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This thesis addresses the tensile capacity and load-deflection behavior of wedge-type expansion and undercut anchors in concrete affected by alkali-silica reaction (ASR). ASR is a chemical reaction that occurs between alkalis in the cement and silica in the aggregates. The reaction occurs with the presence of moisture, forming a gel which expands and causes micro-cracking in the concrete. Researchers conducted 85 static unconfined tensile tests on control and ASR-affected specimens. The results indicate that anchors in concrete cracked due to ASR perform like anchors in concrete cracked due to other mechanisms. Up to a threshold value of the Comprehensive Crack Index (CCI) of at least 1.5 mm/m, all cracking, regardless of cause, has the same effect on the tensile breakout capacity of mechanical and undercut anchors.
Das Buch stellt den aktuellen Stand der kompletten Befestigungstechnik für Beton und Mauerwerk mit Einlegeteilen (Ankerschienen, Kopfbolzen), Dübeln (Metallspreizdübel, Hinterschnittdübel, Verbunddübel, Betonschrauben, Kunststoffdübel) und Setzbolzen umfassend dar. Die Befestigungselemente und ihre Wirkungsmechanismen werden ausführlich beschrieben und das Tragverhalten im ungerissenen und gerissenen Beton untersucht. Weiterhin werden das Korrosionsverhalten, das Verhalten bei Brandbeanspruchung sowie bei Erdbeben- und Schockbeanspruchung behandelt. Von besonderer internationaler Aktualität ist die Bemessung gemäß der europäischen und amerikanischen Normung. Praxisorientierte Kriterien zur Auswahl von Befestigungsmitteln und Bemessungsbeispiele runden das Werk zu einem einzigartigen Handbuch ab.
While significant effort has been dedicated to studying flexural and shear strength of concrete affected by alkali-silica reaction (ASR), bond behaviour and anchorage strength of steel bars and metal anchors embedded in ASR concrete have frequently been overlooked. Bond stress-slip response was studied by means of pullout specimens, both plain and reinforced, to examine the effects of confinement on bond of ASR concrete subjected to different levels of deterioration. Additionally, bond properties in the beam flexural tension regions were also investigated. Lastly, tensile testing of headed bolts cast in unreinforced ASR concrete was conducted as a pilot series of tests. While effect of ASR on the normalized bond strength of confined concrete was negligible, up to 20% reduction in peak bond stresses was observed in unconfined specimens. For the given amount of free expansion, ASR did not detrimentally affect the breakout concrete capacity of anchor bolts embedded in reactive concrete.
Tests were conducted to quantify the effect of alkali-silica reaction on the properties of concrete. Two reactive aggregates, Beltane opal and an amorphous fused silica, were used to simulate the reaction in the laboratory. At 0.1% expansion, concrete containing 5.2 kg/m3 equivalent sodium oxide showed a loss of 12% compressive strength but 50% tensile strength. The compressive strength was not found to be a good indicator of alkali-silica reaction, but the modulus of rupture test proved to be a sensitive and reliable test to identify the progress of the reaction. Dynamic modulus and pulse velocity also appear to be good indicators of alkali-silica reaction. The tests suggest that fused silica is an ideal reactive aggregate to simulate expansion due to alkali-silica reaction, and that it provides an effective means of determining the deterioration in concrete properties and in evaluating mineral admixtures to control expansion.
The influence of reinforcement on the development and distribution of multiaxial expansions in reinforced concrete elements due to alkali-silica reaction (ASR) requires further research. Understanding how passive restraint provided by reinforcement in a given direction may simultaneously affect expansions in that direction as well as in other reinforced or unreinforced directions is important for assessment of ASR-affected structures. Few experimental studies to date have endeavored to monitor expansions in more than one direction for field-scale reinforced concrete specimens. A parametric study at The University of Texas at Austin was conducted in which thirty-three 19 in. reinforced concrete cubes were fabricated and monitored for ongoing ASR expansions. The cubes had variable uniaxial, biaxial, and triaxial reinforcement layouts and ratios. Three concrete mixtures of varying reactivity, controlled by altering the types of coarse and fine aggregate, were used. The cubes were conditioned in an outdoor, climate-monitored environmental facility and were regularly measured in three orthogonal directions to track expansions. The expansions monitored physically corresponded to micro- and macro-cracks that form due to ASR. The specimens exhibited typical surface cracking due to ASR. Random “map cracking” occurred on the surfaces of the triaxially restrained and unreinforced specimens. Large, discrete surface cracks formed between layers of reinforcement for the uniaxially and biaxially restrained specimens as the specimens expanded in the unreinforced directions. Cylinder tests were performed over the course of the program to gauge material property degradation due to ASR-induced expansions; however, due to the small size and fluctuating conditioning of the cylinders the results from these tests were not considered representative of the material property degradation associated with the cube specimens. Prism expansion monitoring was used to predict the free expansion potential of the cube specimens under idealized ASR conditioning. However, much like with mechanical property degradation, the small size and differential conditioning of the prisms limited effective correlation of prism expansions to cube specimen expansions. This study primarily focused on the development of ASR-induced reinforced concrete expansions over time. Cubes fabricated from the three mixes exhibited variable expansions due to the different reactivities of the coarse and fine aggregates; however, the use of different mixes did not change the overall axial expansion distribution trends documented across all specimens. Expansions in unreinforced directions exceeded those of the reinforced directions in all specimens. The rate of expansion of the reinforced directions of the uniaxially and biaxially restrained specimens was reduced once the expansion of the restrained axes reached and exceeded the steel yield strain. The unreinforced and triaxially reinforced specimens exhibited similar proportional axial expansions in all directions; however, the reinforcement did reduce expansions. Analysis of the axial distribution of volumetric expansions, i.e. the summation of the axial expansions, made it possible to remove the influence of concrete mixture reactivity and variable moisture and temperature conditioning during the timeline of specimen production and placement within the storage facility. The axial expansion distribution trends depicted the axial expansions influenced by the reinforcement and not the conditioning of the specimens. This permitted the development of expansion trends that were solely impacted by axial reinforcement conditions, and were independent of other extraneous factors.
Alkali-Silica Reaction (ASR) is considered one of the most significant critical internal deterioration mechanisms for concrete. ASR produces internal stresses that causes expansion and extended cracks threatening the country's wealth of existing infrastructure. Since ASR recognition in 1940 by Stanton, many studies had been conducted to evaluate the degree of reactivity for different types of gravel. However, limited research has focused on studying the effect of specimens' shape and size, and casting direction on the accuracy of measured ASR expansion and find a correlation between cylindrical and standard prismatic specimens. Moreover, few studies have attempted to evaluate the optimum expansion level for controlling ASR expansion by strengthening ASR-damaged concrete. An experimental work divided into three phases was conducted to evaluate; (1) The effect of these new approaches on ASR expansion using fused silica (FS) as a fast-acting material, (2) The selection of a suitable jacketing materials based on target performance rather than focusing only on the achieved strength investigating concrete mixtures incorporating four types of fibre and fine crumb rubber aggregates (FCRA) with and without silica fume, (3) The effectiveness of six different strengthening materials as CFRP, BFRP, mortar with GG mesh, mortar with BFRP mesh, FRC, and CRC with BFRP to suppress ASR expansion, and evaluate sensitivity of strengthening time and testing time vs. the strengthening types on the concrete mechanical properties. The results exhibited addition of FS caused a drastic increase in the expansion, and plays a crucial role to adversely affect concrete mechanical properties and durability index until age 180 day, then the effectiveness decreased until 548 days. Specimen geometry and size, and casting direction had a significant effect on the rate of expansion. Cylindrical specimens expanded at a higher rate than the prisms until 56 days in the range from 43% to 37%, and from 9% to 15% at 90 days until test termination at 548 days. Specimens cast vertically exhibited an increase in expansion over the others cast horizontally in the range from 2.63% to 8.41%. Specimens Ø100×200mm reveal lower expansion in the range from 5.89% to 9.52% than specimens Ø75×285mm. Concrete mixtures incorporating steel, macro, and micro polypropylene, micro nylon fibres, and FCRA with and without SF were examined. Based on balancing between mechanical properties, durability indices, and electrical resistivity, FRC incorporating micro polypropylene with SF, and CRC contained FCRA with silica were selected as FRC and CRC jacketing. Strengthening type, strengthening time, and testing time after applying strengthening materials showed a significant effect to control ASR expansion and enhanced the damaged concrete properties. For instance, CFRP exhibited a significant reduction in expansion compared to that with control specimens and followed by BFRP, CRC with BFRP, Mortar with GG, Mortar with BFRP, and FRC, respectively. Moreover, strengthening at early ages revealed decreases mechanical properties as a result of high residual expansion. However, testing at early ages showed higher results proved the exposure conditions had an adverse effect on the strengthening materials.
Alkali-silica reaction, or ASR, is a common deterioration mechanism that subjects concrete to internal expansive stresses. Previous research on the structural effects of ASR has shown that if a structure is effectively confined by reinforcement (e.g., three-dimensional reinforcement configuration), it is unlikely that its performance will be compromised by the development of ASR. On the other hand, in structures that are not effectively confined by reinforcement (e.g., no transverse reinforcement present, such as slabs and walls), unrestrained expansion occurs in the direction that is lacking restraint, possibly introducing a structural vulnerability. Multiple laboratory studies have been conducted to identify the structural implications of ASR in reinforced concrete. However, large-scale tests on ASR-damaged concrete elements without transverse reinforcement have not been found in the literature and the structural implications of ASR on that type of elements therefore remain uncertain. The research described in this dissertation studied the effects of ASR-related damage on the shear behavior of full-scale structural concrete elements without transverse reinforcement. The main objective was to quantify the effects that different severity levels of ASR had on the shear strength and behavior of the test specimens. This objective was accomplished through a full-scale experimental program. A total of ten specimens modeled after typical structural walls were fabricated in the laboratory and subsequently tested in shear, at different target levels of ASR expansion. The development of ASR was facilitated through the use of known reactive materials and aggressive conditioning regimes. The progress of specimen deterioration was monitored and correlated to structural test results. Structural test results did not reveal any deficiencies in the shear performance of the specimens at any level of ASR-related expansion examined in this test program. Based on the results of this research, several recommendations were made for the assessment of ASR-related deterioration and residual shear strength of ASR-affected structures in the field
Alkali-silica reaction (ASR) is a chemical reaction between the alkali hydroxides from the concrete pore solution and some siliceous mineral phases present in the aggregates used to make concrete. ASR generates a secondary product, the so-called ASR-gel, that swells upon moisture uptake, leading to induced expansion, microcracking, and reduction in the mechanical properties of the affected material. ASR is likely the most harmful damage mechanism affecting the serviceability and long-term performance of concrete infrastructure worldwide, yet its structural implications in concrete structures remain unclear. Even though shear resistance of reinforced concrete has been studied extensively by the research community due to the brittleness and danger associated with concrete shear failures, knowledge on the impact of ASR on reinforced concrete shear resistance is very limited. To fill this lack of knowledge, the effect of ASR on the aggregate interlock shear transfer mechanism in reinforced concrete was investigated. Lightly reinforced shear push-off specimens with low to moderate expansion levels were tested while recording crack kinematics. The experimental testing program allowed to decouple the deleterious effect of ASR microcracks within the reactive coarse aggregate particles and the beneficial effect of the so-called chemical prestressing. The aggregate interlock shear strength was significantly impacted, even in the case of a low expansion level for which the microcracks have theoretically not reached the cement paste yet, and surprisingly, it was not affected by prestressing. The experimental results were compared to predictions from three existing simplified aggregate interlock models which tended to overestimate the measured shear strengths. Digital image correlation (DIC) is an innovative optical measurement technique that could provide several advantages for long-term structural inspections such as remote full-field measurements. A method was proposed to correct 2D-DIC measurement errors associated with the inevitable camera movement between photographs taken during different inspections. Using the aforementioned push-off specimens, it was applied to the monitoring of shear crack kinematics and ASR expansion. The method significantly improved measurements produced from images acquired with a non-expensive hand-positioned camera equipped with a lens of normal focal length and a free to use DIC software. For ASR expansion monitoring, the measurement errors could not be reduced below a selected tolerance limit of ±0.02 mm (±0.01% strain), although increasing the measurement gauge length could potentially provide satisfactory results. On the other hand, over 99 and 96% of the measurements were within the selected tolerance limit of ±0.1 mm for the corrected crack width and slip measurements, respectively. These promising results validate the potential of the proposed method to overcome errors associated with camera movement between photographs and as such, it represents a step towards the use of the DIC technique for periodic structural inspections.