Maryangela Geimba de Lima

Service life of concrete structures considering the effects of temperature and relative humidity on chloride transport

Chloride is one of the main factors responsible for damages related to the corrosion of the concrete reinforcement in marine environments. It is known that this mechanism of degradation is directly related to environmental variables. Within this context, it can be inserted the global climate change. This paper deals with the effects of temperature and relative humidity changes on the service life of concrete structures affected by chloride attack. This way, three situations of environmental aggressiveness were simulated: past, current, and future. Then, models for predicting the chlorides penetration were analyzed to the three selected situations. So, a practical methodology is presented, and the results are consistent with the literature data. Among the results, it can be noted that changes in temperature and relative humidity identified in a period of 100 years were responsible for a reduction from 7.8 to 10.2 years of service life. Most standards provide a design service life of 50 years for reinforced concrete structures.

Influência do ambiente natural sobre o ambiente construído: um estudo sobre o índice de chuva dirigida

This work analyzes environmental factors (rain and winds) range and its influence under the buildings. The results for the analyzed period (2000-2010) showed a considerable variation among the maximum and minimum index to Brazil and could support adaptation of technical standards for buildings in order to increase their lifetime, and consequently reduce the impact over the built environment.

Influence of Distinct Curing Environments on the Compressive Strength of Concrete

This paper discusses the influence of different curing conditions on the compressive strength of concrete test specimens monitored for 365 days. Five cures were analyzed. Statistical tests were applied (variance analysis and Fisher’s) in order to evaluate the data. According to results, different curing conditions influence the compressive strength of concrete. The main novelty of this article is that the curing conditions affect the concrete compressive strength significantly only for ages over 28 days. Furthermore, this study shows that concrete specimens saturated with water have superior strength to concrete cured in a standard environment (moist chamber). The compressive strength of concrete decreases, respectively, with the following types of curing investigated: water tank, moist chamber, tank with water and lime, laboratory internal environment and external environment. The compressive strength gain over time also varies for each condition. The lower values found for the external environment confirm the greater difficulty of controlling the water loss on this environment, resulting in decrease of compressive strength.

Self-healing of self-compacting concretes made with blast furnace slag cements activated by crystalline admixture

Test samples were examined using a specific crystalline admixture, AR glass fibre and three types of cements with percentages of blast furnace slag (BFS) of 55%, 35% and 0%. Test specimens were loaded under compression until 90% of their failure load, in order to generate a network of micro-cracks. These samples were subsequently immersed in lime water to trigger the self-healing mechanism, followed by various tests at 28, 56 and 84 days. As BFS content ratio was increased to 55%, there was a noticeable increase in mechanical recovery and permeation reduction properties, indicating good self-healing.

Applicability of recycled aggregates in concrete piles for soft soil improvement

The expressive generation of construction and demolition waste is stimulating several studies for reusing this material. The improvement of soft soils by concrete compaction piles has been widely applied for 40 years in some Brazilian cities. This technique is used to improve the bearing capacity of soft soils, allowing executing shallow foundations instead of deep foundations. The compaction piles use a high volume of material. This article explored the possibility of using recycled aggregates from construction waste to replace the natural aggregates in order to improve the bearing capacity of the soft soil, regarding its compressive strength. Construction wastes from different stages of a construction were used in order to make samples of concrete with recycled aggregates. The strength of concretes with natural aggregates was compared with the strength of concretes with recycled (fine and coarse) aggregates. Results show that all samples met the minimum compressive strength specified for compaction piles used to improve the bearing capacity of soft soils. The concrete with recycled aggregate from the structural stage had even higher resistances than the concrete with natural aggregates. This behaviour was attributed to the large amount of cementitious materials in the composition of this type of concrete. It was also observed that concrete with recycled fine aggregate has a superior resistance to concrete with recycled coarse aggregate.