Ronaldo A. Medeiros-Junior

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.

Repair Mortars Incorporating Multiwalled Carbon Nanotubes: Shrinkage and Sodium Sulfate Attack

AbstractThis study investigates the effect of multiwalled carbon nanotubes (MWCNTs) on the shrinkage and expansion caused by sodium sulfate attack in repair mortars; repair mortar behavior in the f...

Impact of climate change on the service life of concrete structures

Abstract Degradation processes reduce the service life of concrete structures, resulting in social, environmental and economic damage. Many of these processes are closely related to the climate variables of the external environment. Oftentimes, investments for repair and maintenance is required when the durability of a concrete structure is compromised, resulting in high costs for a country’s economy. The main climate variables that interfere with the concrete degradation mechanisms are: temperature, relative humidity, precipitation, wind, waves and tides. The knowledge about the performance of the environmental variables in the degradation mechanisms needs constant updating, mainly due to climatic changes. Climate changes are any changes in weather over time that remain for a long time. This issue has become of great concern in practically all sectors of society, since the consequences of climate changes are already present on the planet Earth. This chapter discusses some effects of climatic variables on concrete durability. Some scenarios of climate change are also discussed. An example of a numerical application about the corrosion of reinforcements on the Brazilian coast is applied. This chapter shows that, mainly in the long term, climate change can contribute to reducing the service life of concrete structures.

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.