## 2 In Situ Strength Assessment
### Pucinotti Method  
In [13], an analytical and alternative formulation was proposed in order to estimate the in situ characteristic concrete compressive strength based on a series of destructive laboratory tests on 359 cores. In this paper, the analytic expression is updated with the addition of new coefficients in order to consider the following aspects: (i) the presence of reinforcing bars in the cores; (ii) the moisture condition of the core; (iii) the age of the concrete at the time of the coring.  
Therefore, the average value of the in situ compressive strength is calculated by the following equation:  
\[f_{cm,a,P}=\left(\sum_{i=1}^{n}\alpha_{2}^{i}\cdot C_{dia}^{i}\cdot C_{d}^{i} \cdot C_{l/d}^{i}\cdot C_{steel}^{i}\cdot C_{mc}^{i}\cdot C_{t}^{i}\cdot f_{core, i}\right)/n \tag{2}\]  
in which:  
* \(\alpha_{2}\) depends on the drilling direction (\(\alpha_{2}=1.15\) for drilling perpendicular to the direction of casting concrete, and \(\alpha_{2}=1.05\) for perforations parallel to the direction of casting concrete);
* \(C_{dia}\) takes into account the diameter of the core: 1.06 for the core diameter with \(d\) = 50 mm, 1.00 for \(d\) = 100 mm, and 0.98 for \(d\) = 150 mm;
* \(C_{d}\) takes into account the disturbance during drilling operations. It presupposes the following equation:  
\[C_{d}=-0.006\cdot f_{core}+1.26 \tag{3}\]  
where \(f_{core}\) is expressed in MPa;
* \(C_{l/d}\) takes into account the ratio height/diameter (\(l/d\)) of core. It presupposes the following equation:  
\[C_{l/d}=0.045\cdot(l/d)^{3}-0.308\cdot(l/d)^{2}+0.766\cdot(l/d)+0.340 \tag{4}\]  
in which \(d\) is the core diameter and \(l\) is its height.
* \(C_{steel}\) takes into account the presence of reinforcing bars. According to the British Standards Institution (1991), for cores containing a single bar, \(C_{steel}^{i}=1+1.5\frac{\partial\cdot b}{d\cdot l}\), where \(\phi_{r}\) is the diameter of the reinforcement. \(b\) is the distance of the axis of the bar from nearer the end of the specimen; \(d\) and \(l\) are the diameter and the length of the specimen after end-preparation by grinding or capping, respectively. The results should be ignored if the correct strength varies more than 10% [1]. In the case of several bars: \(C_{steel}^{i}=1+1.5\frac{\sum\phi_{r}\cdot b}{d\cdot l}\). Personally, I believe that, in general, it would be advisable to always discard the cores that incorporate reinforcing bars inside.
* \(C_{mc}\) takes into account the moisture condition of the core. According to ACI 214.4R-03 [17], the following values are suggested: (i) as-received, \(C_{mc}\) = 1.00; (ii) soaked 48 h, \(C_{mc}\) = 1.09; (iii) air dried, \(C_{mc}\)= 0.96.
* \(C_{t}\) takes into account the age of the concrete. For young concrete, that is, if the tests are carried out before 28 days of curing, then the value suggested by EN 1992-1-1 [7] could be used: \(C_{t}^{i}=\frac{1}{\rho^{i}(1-\sqrt{28/t})}\), where \(s\) is a coefficient which depends on the type of cement. (i) \(s\) = 0.20 for cement of strength classes CEM 42.5 R; CEM 53.5 N; CEM 53.5 R (Class R). (ii) \(s\) = 0.25 for cement of strength classes CEM 32.5 R; CEM 42.5 N (Class N). \(s\) = 0.38 for cement of strength classes CEM 32.5 N (Class S). This expression allows us to extrapolate the strength measured before 28 days (of young concrete) to that at 28 days. Some authors suggest also using this coefficient for concrete with an age \(t>28\) days [10] to take into account the greater strength of concrete after 28 days.