3. Nondestructive testing methods

Nondestructive testing (NDT) methods are widely used in the investigation of the mechanical properties and integrity of concrete structures. As seen in Table 1, provided by AASHTO [8], the following techniques are used for detecting defects in


#### Table 1.

Capability of investigating techniques for detecting defects in concrete structures in field use [8].

concrete structures for field use. In the present study, ultrasonic pulse velocity (UPV) method is used to evaluate the properties of LWC. Ultrasonic techniques measure the velocity of a pulse, generated from a piezoelectric transducer in concrete, and this measurement assesses the mechanical properties of a concrete. Based on research and correlations, the pulse velocity relates items such as compressive strength or corrosion [1]. As seen in Table 1, UPV detects corrosion in reinforcement; however, it is not studied in this report.

correlation between fc and UPV will be an enhancement for inspection and assess-

Therefore based on the previous studies, it is recommended that for each type of LWA used in LWC, the researchers conduct an experimental program to drive a brand new relation between UPV and compressive strength of concrete, which is not the focus of the present chapter. Hence in the present chapter, we have presented some of the most recent proposed equations, relating UPV to compressive strength of LWC, and presented some of the available equations relating UPV to compressive strength of LWC and NWC for those interested to compare the configurations of the equations and to initial their research for the specific types of

During the last decades, many researchers presented different methods for the evaluation of compressive strength for LWA concrete versus UPV. The LWA in those studies consists of different types of natural or man-made LWA such as recycled lightweight concrete aggregates (RLCA), light expanded clay aggregate (LECA), high-impact polystyrene (HIPs), granulated ash aggregate (GAA), granulated expanded glass aggregate (GEGA), foam expanded glass aggregate (FEG), expanded clay aggregate (ECA), and expanded glass aggregate (EGA). In the literature several factors that influence the relation between compressive strength and UPV were examined. Most important analyzed factors included the cement type and content, amount of water, type of admixtures, initial wetting conditions, type and volume of aggregate, and the partial replacement of normal weight coarse and fine aggregates by LWA. As a result, simplified expression was proposed to estimate the compressive strength of different types of LWAC and its composition. The dependence of UPV and the modulus of elasticity were also explored in many of works [13]. They presented the expression below for a wide range of SLWC with compressive strength varying from 20 to 80 MPa. UPV and density are measured in

equal to 54.6, 54.3, 0.86, etc. and is a correlation coefficient. Values of UPV and strength measurements were performed on cubed concrete specimen in their study:

fc <sup>¼</sup> UPV

Kupv ∗ p<sup>0</sup>:<sup>5</sup> <sup>2</sup>

where fc is the compressive strength of concrete (MPa), UPV is the ultrasonic pulse velocity (m/s), KUPV is a constant representing the correlation coefficient,

[9], equations for LWC containing fibers were proposed to estimate the concrete compressive strength from respective UPV values. The equations presented below

where fc is the compressive strength of concrete (MPa) and v is the pulse velocity (m/s). Other types of equations were presented in 2015 [10], which contributed the coarse aggregate content as a ruling factor in the relationships presented. In the developed equations, the fc was represented for a compressive cube strength measured in MPa. The variable, v, is UPV and it was measured in

are the compressive strength of concrete at days 7 and 28, respectively:

. From the regression analysis, Kupv can be a constant

). In the research presented elsewhere

(1)

3

<sup>f</sup> <sup>c</sup> <sup>¼</sup> <sup>1</sup>:269 exp :ð Þ <sup>0</sup>:841v 7 days (2) fc <sup>¼</sup> <sup>0</sup>:888 exp :ð Þ <sup>0</sup>:88v 28 days (3)

ment of structures made of LWC.

Compressive Strength of Lightweight Concrete DOI: http://dx.doi.org/10.5772/intechopen.88057

3.2 Utilizing UPV to find the compressive strength

LWA of interest.

meters per second and kg/m<sup>3</sup>

55

and ρ is the dry density of specimen (kg/m<sup>3</sup>
