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

ABSTRACT/ INTRODUCTION:

This work is aim 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 below, 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 below 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.

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.

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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The first case assigned to the DEF as main cause factor of damage happened in 1987, in Finland, affecting concrete precast sleepers that had been subjected to an improper heat treatment and exposed to moisture. Beyond Finland, other countries in the world also reported this phenomenon in sleepers and in various different types of precast elements after about 10 years of operation (LCPC). Apart from precast components, the DEF was also responsible for damaging several bridges in Britain, ranging between 8 to 20 years after construction.

The scanning electron microscope can show the elements in in ettringite gel as well as silica gel and can give indirect information about mineralogy. Concrete investigators at the Minnesota DOT have developed other techniques for measuring ettringite in concrete.

Is it OK to have air voids partially full of ettringite gel if the pavement is able to perform adequately? What is an adequate service life for PCCP? In Iowa, the best concrete aggregates are expected to perform for 30-40 years, even when deicing salts are used on the PCCP. Should air voids also function as reservoirs for excessive ettringite gel? Do you go after the source of the problem or do you use remedial techniques?

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