Experimental analysis of the spalling phenomenon in precast reinforced concrete columns exposed to high temperatures

Abstract

Among the processes that involve the degradation of concrete structures subject to the high temperatures of a fire there is the spalling phenomenon. Its mechanisms are related to the thermal stress of the materials dilatations and pore pressure the process of vaporization of water during heating. The factors that influences in its occurrence are related to concrete properties, structural member characteristics or the exposure conditions, and their parameters are not clearly known yet. This paper aimed to study the influence of three concrete mixtures, four coating thicknesses and two bars diameters of longitudinal reinforcement in the spalling phenomena exposed to ISO 834 fire curve. The characterization of concrete were performed either of the axial compression strength tests, water absorption by capillary and mercury intrusion porosimetry, besides the fire resistance tests in real-scale specimens. It was concluded that the diameter of the bar does not have influence, while the mixture and the concrete cover thickness does. More spalling was recorded for the columns with thicker concrete cover and concrete compressive strength at 61,9 MPa, and although higher strength concrete have less permeability, this characteristic can be balanced with the higher tensile strength of this type of concrete.

A Review of Precast Concrete Beam‐to‐Column Connections Subjected to Severe Fire Conditions

“…Spalling is the breakaway of a layer of concrete from the surface as a result of the high internal steam pressure from water vaporisation [30,38,39]. Spalling can be categorised as aggregate spalling, explosive spalling, surface spalling, and corner/sloughing-off spalling, as shown in S1, S2, and S3.…”

“…Despite the high strength and excellent durability of this concrete, its low permeability proves to be a disadvantage at high temperatures. e structural performance of reinforced concrete structures is influenced primarily by spalling, which causes loss of material, smaller cross-sectional areas (∆d), and exposure of the reinforcing steel to excessive temperatures, as shown in Section 1-1 [30,38,39,41]. Researchers have elucidated the critical role of spalling in reducing the fire resistance of a structure [42,43].…”

Análise das resistências ao escoamento (fy) e de ruptura (fu) residual das armaduras de pilares de concreto em altas temperaturas

“…Ainda, as barras com diâmetros maiores expandem e produzem tensões no interior dos elementos de concreto, o que aumenta a probabilidade de ocorrer o desplacamento deste, conforme Morita (2000), Majorana (2010) e Bolina (2016). O desplacamento manifesta-se por meio da perda de camadas superficiais do cobrimento, que pode ocorrer de maneira explosiva ou progressiva (GIL et al, 2018). Essa perda de seção decorre das tensões que se desenvolvem no interior do elemento, devido às dilatações térmicas diferenciais de seus componentes e ao processo da saída de vapor da água (FELICETTI; LO MONTE, 2013).…”

Efecto del spalling sobre la resistencia a flexión biaxial de pilares de hormigón armado expuestos a fuego.

“…Este desprendimiento, violento o no, de las capas o trozos de hormigón más superficiales de un elemento estructural se da cuando, además de estar expuesto a altas temperaturas, la velocidad de calentamiento es alta, con velocidades típicamente de 20-30ºC/min [1]. Cuando aparece durante los primeros 30 minutos de exposición al fuego puede llegar a ser de carácter explosivo [2,3]. Sin embargo, la manera en que se manifiesta a…”

“…Existe un debate abierto sobre la probabilidad de aparición del spalling y las causas que lo producen. Los parámetros que influyen en la aparición del mismo son: la humedad de la masa de hormigón, la velocidad de calentamiento, estado tensional previo, la permeabilidad, la resistencia a compresión del hormigón, el recubrimiento y separación de las armaduras o el método de vibrado del hormigón [2][3][4]. Casi todo lo que se conoce acerca del spalling en el hormigón viene de la experiencia y observación de edificios y otras estructuras expuestas a fuego [5].…”