How To Prevent Building Collapse, Cracks And Pile Caps Foundation Failures in A Metropolitan Areas Part 1: SWAB Builders 08143352493

Keywords: delayed ettringite formation (DEF); chemical composition; temperature; prevention; risk; and concrete deterioration.

ABSTRACT/ INTRODUCTION:

This work aims at providing a delayed ettringite formation (DEF) in pile caps foundation risk analysis with critical diagnosis on temperature, concrete deterioration and causes lead to failures of mechanical property at Metropolitan areas with a case studies of Recife Region - PE - Brazil and Lagos metropolitan area of Nigeria.

Weather in Recife:

The graph below shows average temperature and monthly accumulated precipitation in Recife, capital of the State of Pernambuco, in Brazil.

In the graph above, the orange line shows temperature in degrees Celsius; the blue bars show precipitation in millimeters of raining.

Source of information: Brazilian Institute of Aerospace Research - Weather Forecast Department.

While in Lagos, Nigeria:

The graph shows that:

1) Average temperature in Recife is high, and has little variation along the year. During the summer, temperature is about 27 degrees Celsius, and during the winter, it has a slight drop to around 24 degrees.
2) There is a concentration of rain during the period March through August.
Total annual Precipitation averages 1506.6 mm (59.3 inches) which is equivalent to 1506.6 Litres/m² (36.95 Gallons/ft²).On average there are 1885 hours of sunshine per year. Visit the sunshine and daylight section to check monthly details including how high in the sky the sun reaches each month.Were you to burrow down through the centre of the Earth from Lagos you would pop up nearest to the climate station at Apia, Upolu, Samoa where you would find a Tropical wet climate.

ABSTRACT

Currently, there is an awareness that is critical to assess the durability characteristics of concrete with as much attention as the mechanical properties. The durability of concrete structures can often be affected by chemical attacks, jeopardizing its performance and security.

When concrete is subjected to high temperature at early ages, many physical and chemical changes in hardened concrete may occur. It is widely accepted that concrete subjected to these conditions of temperature and exposed to moisture is prone to cracking due to Delayed Ettringite Formation (DEF).

Temperature rise measurement was performed in situ at 5 different caps through datalogger and thermocouples equipments. Furthermore, the Duggan test was performed in order to assess the level of expansion of 3 cements studied: X (CP II E 40), Y (CP II F 32) and Z (CP V ARI RS). Simultaneously, the chemical compositions of these cements and their respective clinkers were quantified by analysis of X-ray fluorescence (XRF). The cement X (CP II E 40) showed the chemical characteristics favoring with more intensity DEF and, as a result, higher level of expansion in the test Duggan.

It is noteworthy that incorporation of metakaolin (8% and 16%) and silica fume (5% and 10%) showed mitigating potential of expansions. 

It is important to point out that all factors related to thermal properties and chemical composition of the concrete used in the region converge to a condition of ideal susceptibility for triggering DEF. Therefore, it is essential at least minimum and basic requirements in the design specification in order to avoid high temperatures in the massive concrete elements, preventing them from delayed ettringite formation.

1. INTRODUCTION:

Currently in Brazil, just like any other metropolitan areas there is a growing concern about the durability of structures in reinforced concrete as far as the mechanical performances of these structures.

So, it was recently published: The Performances Standard - NBR 15575:2013 - Edificações Habitacionais - Desempenho, which specifies a level of minimum performances regarding a service life for the systems principals that make up the residential buildings (ABNT.

In turn, the durability of concrete structures can often be affected by chemical attacks, endangering its performance and safety. The two main chemicals attacks to concrete are attributed to Alkali-Aggregate Reaction (AAR) and the action of sulphates, among which stands out the Delayed Ettringite Formation (DEF - Delayed Ettringite Formation).

Due to the severity and the great number of reported cases of deterioration attributed to the RAA, currently, in Brazil, has numerous academic researches and case studies of affected structures, in order to try to eliminate or mitigate the risks of emergence the AAR (HASPARYK [2].

Commonly, the deterioration of many concrete structures has been attributed only and exclusively to the AAR. In fact, what can be there, in many cases, is a combination of attack mechanisms, such as DEF, who also presents very similar symptoms to the AAR, which may impair diagnosis and prognosis of the problem (HASPARYK et al.      

Unlike the AAR, the DEF phenomenon has few reports in Brazilian literature, like the jobs of Melo [4] and Melo et al. [5-6]. Until then there is no standardization and national guidelines of prevention related to the DEF, apart from that your formation mechanisms are complex and still poorly understood.

This scenario is justifiable to the realization of this work because of the lack of concern or even ignorance on the part of the technical means about DEF. As there is no corrective and economic measure after the triggering of DEF it becomes essential the prevention and control of the factors that trigger this pathology. Therefore, this research explicit the various local factors that influenced and contributed positively to the development of DEF, demonstrating the short importance of your prevention and the creation of a national standardization. 

Among such factors, can be cited: the elevated temperatures reached by massive elements of concrete, due to the cement hydration heat Portland, as it is the case of foundation pile caps, and the chemical composition of cements commonly used in the confection these concretes. 

In this context, the main objective of this paper is to realize a risk analysis of DEF in the confection of pile caps foundation in reinforced concrete of residential buildings in the tropical Metropolitan Regions as to the case studies of Recife (RMR) basing in the LCPC's preventive guide combined with the Duggan's experimental method.

The main hypothesis is that all factors related to thermal properties and chemical composition of the concrete used in the RMR converge for an ideal susceptibility to the triggering the DEF of these foundation pile caps.


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