How To Prevent Building Collapses , Cracks And Pile Caps Foundation Failures in A Metropolitan Areas Part 4 - Fame Agidife @SWAB Group Tel:08143352493

Category of the given structure and the structural part.

Table 1 Examples of structures or structural elements classified by category (adapted from LCPC

2.3.2 Exposure classes relative to DEF

The guide groups the structures, or parts thereof, in three categories that represent the acceptable level of risk related to DEF, as shown in Table 1. The choice of structural category is the responsibility of the designer and depends on the type of structure, its purpose, the consequences of changes in the desired level of security, and lastly, its future maintenance (LCPC.

Table 3 Choice of level of prevention (Adapted from LCPC [7])

Structure category | Exposure class of the structural part	XH1	XH2	XH3
Categoria I	As	As	As
Categoria II	As	Bs	Cs
Categoria

Depending on the degree of exposure of the structural element, the guide defines three exposure classes: XH1, XH2 and XH3 (LCPC [7]). These classes take into consideration the fact of that the presence of water or high humidity is an essential factor for the development of the delayed ettringite formation. Table 2 shows a number of examples of structural elements classified according with their exposure environments.



2.3.3 Levels of prevention

Table 3 shows the four levels of prevention that have been established by the LCPC [7]: As, Bs, Cs and Ds. The prevention level is then determined based on the category and in XH exposure class applicable to said structure.

2.3.4 Precautions adopted based on level of prevention

Each of the four levels of prevention As, Bs, Cs and Ds corresponds to a specific type of precaution to be implemented. The prevention principle is based basically on limiting the maximum temperature Tmax, capable of being reached inside the structure and also, if hit, the maintenance time of this (LCPC) [7].

• Level of prevention As (T max < 85°C)

Table 4 Adaptation to the Brazilian cements of six conditions of use, when the temperature limit is exceeded (Adapted from GODART and DIVET

Condition I	Condition II	Condition III
Duration of the maintenance of the concrete above 75°C < 4 h for Bs and above 70°C < 4 h for Cs; Equivalent active alkalis of the concrete < 3 kg/m³.	1) Use of cements of RS class, with: For precast concrete: In the case of use of cements CP I, CP I S, CP V ARI and CP II F: Equivalent active alkalis of the concrete < 3 kg/m³; For cast in place concrete: CP I, CP I S, CP V ARI and CP II F are not accepted.	Use of cements of type CP III or CP IV; SO3 of cement < 3% and C3A of the clinker < 8%.
Condition IV	Condition V	Condition VI
Use of fly ashes, slags, calcinated natural pozzolans or metakaolin in combination with a cement of type CP I, CP I S or CP V ARI; Additions content > 20%; SO3 of cement < 3% and C3A of the clinker < 8%.	1) Checking of the durability of the concrete with respect to DEF, by mean of the performance test and by satisfying the criteria.	1) For precast elements, the couple concrete/foresight heating is identical or similar to a couple concrete/heating having at least 5 references of use without any problem.

For this level of prevention, the risk relative to the delayed ettringite

formation must be taken into account by means of the following precaution:

n The temperature Tmax capable of being reached within the structure must remain less than 85°C.

n In the case of heat treatment realized in precast elements is authorised to exceed temperature Tmax = 85°C by a rise of up to 90°C, provided that the duration during which the temperature remains above 85°C is limited to 4 hours.

• Level of prevention Bs (T max < 75°C)

For this level of prevention, the risk relative to the delayed ettringite formation must be taken into account by means of the following precaution:

n The temperature Tmax capable of being reached within the structure must remain less than 75°C.

n However, if the maximum temperature reached within the concrete cannot be maintained below 75°C, then it must never exceed 85°C and at least one of the six conditions shown in Table 4 must be satisfied.

• Level of prevention Cs (T max < 70°C)

For this level of prevention, the risk relative to the delayed ettringite formation must be taken into account by means of the following precaution:

n The temperature Tmax capable of being reached within the structure must remain less than 70°C.

n However, if the maximum temperature reached within the concrete cannot be maintained below 70°C, then it must never exceed 80°C and at least one of the six conditions shown in Table 4 must be satisfied.

• Level of prevention Ds (T max < 65°C)

For this level of prevention, the risk relative to the delayed ettringite formation must be taken into account by means of the following precaution:

n The temperature Tmax capable of being reached within the structure must remain less than 65°C.

n If the maximum temperature reached within the concrete cannot be maintained below 65°C, then it must never exceed 75°C with the greeting the following conditions:

n Satisfy the condition II in Table 4; n Validation of the concrete mix design by an independent laboratory with expert credentials in DEF.



Figura 1 Summary flowchart of the experimental sequence

As to the condition VI, a satisfactory reference of use corresponds to the use of a concrete/heating pair for building a structure exposed to conditions that promote DEF development (environment XH2 or XH3) over a significant period of time (at least 10 years), during which absolutely no DEF-related disorder appears. Two concrete/heating pairs are considered to be analogous whenever the concrete mix designs closely resemble one another and especially when the conditions listed below have been met:

n Heating of the project mix design does not surpass heating of the reference design;

n C3A and SO3 contents in the project design cement do not exceed the C3A and SO3 contents of the reference cement ;

n The alkali contents of the two concretes do not differ by more than 10 %;

n Aggregates used in the two concretes are derived from the same origin;

n The component mix contents do not differ by more than 10 %.