W pracy przedstawiono porównanie odporności na powierzchniowe łuszczenie pod wpływem oddziaływania mrozu betonów zawierających trzy typy zbrojenia rozproszonego (włókna syntetyczne, makro-i mikrowłókna stalowe) zastosowane w ilości 0,5 oraz 1,0% objętości mieszanki betonowej, a także betonów bez włókien. Badanie prowadzono na podstawie normy PKN-CEN/TS 12390-9: (2007), metodą Slab test, w warunkach cyklicznych zmian temperatury, w obecności 3% roztworu solnego. Na podstawie wyników badania mrozoodporności określono najbardziej efektywny rodzaj dodatku do betonu w postaci włókien oraz korzystną zawartość. Wykonano dodatkowe badania właściwości fizycznych betonów, takich jak: nasiąkliwość, podciąganie kapilarne roztworu NaCl, gęstość objętościowa.
Knowledge of fracture mechanics parameters can help for a more accurate assessment of frost degradation of high-strength concrete. High strength concretes, despite the tight structure, are characterized by increased brittleness. Cracks in the concrete structure are places of accumulation of significant stresses. Additional stresses resulting from cyclic freeze/thaw stimulate the material destruction processes. The basic strength parameters of concrete do not take into account structural defects of the material and do not give a complete description of susceptibility to damage caused by, e.g., frost degradation. This study aimed to determine the relationship between frost degradation of high-strength concretes and changes in the value of their fracture energy associated with the initiation of cracking after 150, 250, 350 and 450 freeze/thaw cycles. The research was carried out using 100 × 100 × 400 mm samples, with a pre-initiated 30 mm deep notch. The I load model under a three-point bending test was used, based on the procedure recommended by RILEM. Concrete with a compressive strength of 90 MPa with steel fibres and a mixture of steel and basalt fibers was tested. The obtained results allow for the evaluation of frost degradation using fracture energy GF and critical crack tip opening displacement CTODc.
La resistencia a las heladas es una de las características más importantes que describen un elemento estructural de hormigón. En condiciones de procesos de congelación/descongelación frecuentes y repetidos, la estructura se debilita significativamente. Los parámetros físicos que describen el material asumido en la etapa de diseño comienzan a desviarse significativamente de las estimaciones iniciales a medida que avanza la degradación. Con el fin de aumentar la durabilidad de los elementos estructurales expuestos a ciclos de congelación/descongelación, a principios de la década de 1980 se introdujo una nueva generación de hormigones con mejores propiedades de resistencia y durabilidad. Estos hormigones, a pesar de sus muchas ventajas, se caracterizan por una mayor fragilidad y susceptibilidad a la retracción. En este estudio se determinó el efecto de la adición de un 0,5% en volumen de fibras de acero y una mezcla de fibras de acero y basalto sobre la resistencia a las heladas de hormigones con una resistencia de 90 MPa. Se presentó el grado de resistencia de los hormigones al descascarillado superficial en condiciones de tensión durante ciclos de congelación/descongelación. El análisis se basó en las normas ASTM C 666 y PKN - CEN/TS 12390 Slab Test y RILEM. Se determinó el cambio del parámetro que describe la fragilidad y el factor de intensidad de tensión del concreto de alta resistencia debido al ciclo de hielo/deshielo después de 150, 250, 350 y 450 ciclos.AbstractFrost resistance is one of the most important characteristics describing a concrete structural element. Under conditions of frequent, repeatedly occurring freeze/thaw processes, the structure is significantly weakened. The physical parameters describing the material assumed at the design stage begin to deviate significantly from the initial estimates as the degradation progresses. In order to increase the durability of structural elements exposed to cyclic freeze/thaw, a new generation of concretes with improved strength and durability properties was introduced in the early 1980s. These concretes, despite their many advantages, are characterised by increased brittleness and susceptibility to shrinkage. In this study, the effect of a 0.5% by volume addition of steel fibres and a mixture of steel and basalt fibres on the frost resistance of concretes with a strength of 90 MPa was determined. The degree of resistance of concretes to surface scaling under stress conditions during cyclic freeze/thaw was presented. The analysis was based on ASTM C 666 and PKN - CEN/TS 12390 Slab Test and RILEM standards. The change of the parameter describing brittleness and the stress intensity factor of high-strength concrete due to cyclic freeze/thaw after 150,250,350 and 450 cycles were determined.
The paper presents an assessment of the degradation of cyclic freeze/thaw on high-strength concretes, based on changes in the stress intensity factor KIC. The degree of HSC destruction due to cyclic freeze/thaw was determined by the longitudinal modulus of elasticity E, weight loss, and wall strength reduction, determined after 150, 250, 300, and 350 cycles and the total mass of surface scaling after 28 and 70 cycles. The degree of degradation was compared with the modification of stress intensity factor values. Three types of high-strength concretes (compressive strength about 90 MPa) were tested: concrete without fibres, concrete with steel fibres in the amount of 0.5% by volume (39 kg/m 3 ) and concrete with a mixture of steel fibres (19.5 kg/m 3 ) and basalt (6.8 kg/m3). The testing methodology is based on RILEM recommendations [1] and ASTM C666 [2] and PKN -CEN/TS 12390 Slab Test [3].
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