Variations in Mass and Resistance Due to Accelerated Weathering Effects in Concrete Specimens Used in Low-income Housing

Aurora Martínez-Loaiza,María Teresa Sánchez-Medrano

doi:10.13189/cea.2020.080530

Abstract

The reinforced concrete used for construction represents one of the most widely used materials in urban housing. In the case of coastal areas such as Tampico, Tamaulipas, Mexico, the behavior of the concrete elements used in housing differs from less aggressive environmental areas, as evidenced by the built heritage. This work presents results in relation to causes-effects of environmental loads such as humidity, temperature, solar radiation, acid rain and carbonation on specimens of hardened concrete with f'c of 20 and 25 MPa, especially in aspects such as variations in mass and durability and even decreased early resistance. The tested specimens show a variety of relationships that illustrate the effect of the studied parameters, before and after being subjected to accelerated weathering tests; additionally, durability aspects were considered on 6 slab models designed and built to microscopically visualize fissures in the exposed faces, registering mechanical resistance through periodic monitoring that is still maintained. The study showed that concrete with f´c of 20 MPa has greater mass losses and advances in the carbonation front after being exposed in an artificial accelerated aging chamber (AAA), as well as greater degradation when exposed to sulfuric acid, although with less adhesion of salts.

Highlights

Concrete is a material commonly used in construction, due to its mechanical characteristics, its versatility and the geometry it can adopt, its durability depends on the environmental characteristics in which it is found
From the inspection carried out on the surfaces of the concrete slabs, only contraction fissures were identified that originate from the rapid loss of water on the concrete surface before it sets, and they are unsightly, they are not usually related to structural damage, their presence can generate the entry of moisture and the reproduction of microorganisms such as mites over time, which could be observed through the microscope during the measurement process
This condition can be related more to the construction process than to the design resistances, because the evaporation rates at the surface are affected by the wind speed as well as by the high environmental and concrete temperatures; variables that were not controlled, considering that only in the first slab built with a design fc of 20 MPa the greatest number of fissures appeared and that in none of the slabs was the width greater than 0.5 mm throughout the 18-month observation period, In each of the beams tested in flexion, the failure occurred in the central third, calculating the modulus of rupture with the corresponding equation for this case

Summary

Introduction

Concrete is a material commonly used in construction, due to its mechanical characteristics, its versatility and the geometry it can adopt, its durability depends on the environmental characteristics in which it is found. Acids are compounds that can reduce the useful life of concrete because it reacts with carbonates and in turn modifies the resistance [5], which damage the interface of heterogeneous elements. Other components can modify the behavior of concrete mainly when it is armed with steel [6] that interacts producing corrosion which crystallizes with changes in volume and producing cracks. Studies have been carried out to know the effects of carbonation on the durability of concrete and some models to produce the effects on its morphological changes [7] [8] as well as the formation of fissures through which degrading compounds can be introduced and use of some additives [9]

Objectives

Results

Conclusion