Page 308 - New Trends in Eco efficient and Recycled Concrete

270 New Trends in Eco-efficient and Recycled Concrete

The design values of ultimate moment and shear resistance are larger or at least equal to
design values of bending moment and shear force, respectively.
The limiting value of crack width is:
w max 5 0:4 mm for XC1

w max 5 0:3 mm for XC3

The limiting value of deflections for quasi-permanent load is:
l
v max 5
250
where l is the slab span;
The design working life of 50 years was assumed (‘normal’ supervision during execution
and ‘normal’ inspection and maintenance during use).
The standard fire resistance REI 60 was considered due to the limited dimensions of the
building; therefore, according to Eurocode 2 Part 2 for continuous solid slabs:

h s;min 5 80 mm

a min 5 10 mm

where h s is slab thickness and a is the axis distance of reinforcing steel to the near-
est exposed surface.
All the properties and equations used in the design of floor slabs are summarised
in Table 10.5. Designations and meaning of parameters in Table 10.5 completely
follow notations and equations used in Eurocode 2 Parts 1 and 2.
The measured concrete strength in selected tests was considered as mean con-
crete compressive strength f cm . For NAC mixes, the 28-day characteristic compres-
sive strength f ck , tensile strength f ctm , modulus of elasticity E cm and creep
coefficient ϕ(t,t 0 ) were calculated according to Eurocode 2 Part 1 provisions,
Table 10.5. For RAC mixes, the 28-day characteristic compressive strength f ck and
tensile strength f ctm were also calculated according to Eurocode 2 Part 1 provi-
sions. It has been shown in previous extensive research that the relationship
between compressive and tensile strength given in this standard is valid, with the
same reliability level, for RAC mixes (Silva et al., 2015).
However, it is now well-known that RAC mixes have a lower modulus of elas-
ticity and exhibit larger creep compared to companion NAC mixes. Various propo-
sals for prediction models were published in literature and prediction models
presented in Lye et al. (2016) for RAC modulus of elasticity and for RAC creep
coefficient were selected in this work. So, for modulus of elasticity following rela-
tionship was obtained (Lye et al. 2016):

E cm;RAC1;2 5 0:82E cm;NAC1;2 (10.7)