3.1 Ultrasonic pulse velocity (UPV)

AASHTO states that the accurate measurement of the concrete's strength depends on several factors and is best determined experimentally [8]. In the present work in addition to the conventional compression test, UPV is utilized to explore the properties of concrete. In general UPV tests are used to distinguish the material and integrity of concrete sample being tested. This technique enhances quality control and detection of defects. In the field, UPV verifies concrete uniformity, detects internal imperfections and finds the imperfections' depth, estimates the deformation moduli and compressive strength, and monitors characteristic variations in concrete throughout time [9]. From observations, certain factors influence UPV. The theory for elasticity for homogeneous and isotropic materials states that the pulse velocity of compressional waves (P-waves) is indirectly proportional to the square root of the dynamic modulus of elasticity, Ed, and inversely proportional to the square root of its density, ρ [10]. The aggregate type used in a mixture has a significant influence on the elastic modulus; therefore for our current LWA, a significant change in the pulse velocity is expected. To differentiate results, correlations need to be analytically determined. As an example an expression for the modulus of elasticity of concrete and its relation between the compressive strength (fc), the oven-dried density, and the Ec itself is suggested by EN 1992-1-1, Eurocode 2 [11]. This relationship suggests that UPV and fc are not unique and are affected by factors such as the type and size of aggregate, physical properties of the cement paste, curing conditions, mixture composition, concrete age, voids/cracks and moisture content [12]. Factors influencing the UPV method are presented in Table 2 [13]. Constituents of the concrete and its moisture content, age, and voids/ cracks impact UPV significantly. Previous works have shown that a correlation between the compressive strength in concrete and the ultrasonic pulse velocity must be determined for each particular concrete mix [13, 14]. Finding a general


Table 2. Influencing factors for UPV method.

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

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 reinforce-

AASHTO states that the accurate measurement of the concrete's strength depends on several factors and is best determined experimentally [8]. In the present work in addition to the conventional compression test, UPV is utilized to explore the properties of concrete. In general UPV tests are used to distinguish the material and integrity of concrete sample being tested. This technique enhances quality control and detection of defects. In the field, UPV verifies concrete uniformity, detects internal imperfections and finds the imperfections' depth, estimates the deformation moduli and compressive strength, and monitors characteristic variations in concrete throughout time [9]. From observations, certain factors influence UPV. The theory for elasticity for homogeneous and isotropic materials states that the pulse velocity of compressional waves (P-waves) is indirectly proportional to the square root of the dynamic modulus of elasticity, Ed, and inversely proportional to the square root of its density, ρ [10]. The aggregate type used in a mixture has a significant influence on the elastic modulus; therefore for our current LWA, a significant change in the pulse velocity is expected. To differentiate results, correlations need to be analytically determined. As an example an expression for the modulus of elasticity of concrete and its relation between the compressive strength (fc), the oven-dried density, and the Ec itself is suggested by EN 1992-1-1, Eurocode 2 [11]. This relationship suggests that UPV and fc are not unique and are affected by factors such as the type and size of aggregate, physical properties of the cement paste, curing conditions, mixture composition, concrete age, voids/cracks and moisture content [12]. Factors influencing the UPV method are presented in Table 2 [13]. Constituents of the concrete and its moisture content, age, and voids/ cracks impact UPV significantly. Previous works have shown that a correlation between the compressive strength in concrete and the ultrasonic pulse velocity must be determined for each particular concrete mix [13, 14]. Finding a general

Constituents of concrete Aggregate Size Average influence

Humidity degree/moisture content Average influence Other factors Reinforcements Moderate influence

Type High influence

Water/cement ratio High influence

Type of cement Moderate influence

Age of concrete Moderate influence Voids, crack High influence

Cement Percentage Moderate influence

Other constituents Fly ash content Average influence

ment; however, it is not studied in this report.

3.1 Ultrasonic pulse velocity (UPV)

Compressive Strength of Concrete

Table 2.

54

Influencing factors for UPV method.

correlation between fc and UPV will be an enhancement for inspection and assessment of structures made of LWC.

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 LWA of interest.

#### 3.2 Utilizing UPV to find the compressive strength

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 meters per second and kg/m<sup>3</sup> . From the regression analysis, Kupv can be a constant 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:

$$f\mathbf{c} = \left(\frac{\textit{UPV}}{\textit{Kup}\boldsymbol{v}\*\boldsymbol{p}^{0.5}}\right)^{\frac{2}{5}}\tag{1}$$

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, and ρ is the dry density of specimen (kg/m<sup>3</sup> ). In the research presented elsewhere [9], equations for LWC containing fibers were proposed to estimate the concrete compressive strength from respective UPV values. The equations presented below are the compressive strength of concrete at days 7 and 28, respectively:

$$\mathbf{f\_c = 1.269 \,\,\exp\,(0.844\mathbf{v}) \,\,(7\,\text{days})}\tag{2}$$

$$\mathbf{f\_c = 0.888 \ \exp \dots (0.88v)} \tag{28 \text{ days}}$$

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


Table 3.

Proposed equations for finding the compressive strength of concrete using UPV [15].

kilometers per second. The expressions are presented below for different coarse aggregate (CA) contents:

For CA (coarse aggregate content) = 1000 kg/m<sup>3</sup>

$$\mathbf{f\_c = 8.88 \,\exp\,(0.42v)}\tag{4}$$

The NWA's absorption capacity, specific gravity, and moisture content are evaluated according to ASTM C 127-01 [17] and ASTM C 566 [18]. Table 6 includes aggregate properties such as specific gravity, absorption capacity, moisture content, and fineness modulus (FM). In Figures 1 and 2, the individual aggregates are shown. The maximum normal weight aggregate size was 9.53 mm (3/8″).

Sieve size Weight retained (kg.) % retained % coarser % finer 19 mm 0 0 0 0 13 mm 0 0 0 0 9 mm 0.047 2.073 2.073 97.93 No. 4 1.6 70.49 72.56 27.4 No. 8 0.5 21.622 94.18 5.82 No. 10 0.021 0.92 95.1 4.9 Passing 0.112 4.9023 99.99 0.001

Sieve analysis Sample size (SS): 1000 g

Sieve analysis Sample size (SS): 2.27 kg

Property Normal weight aggregates Lightweight aggregates

Coarse sand (CS)

Fineness modulus 3.64 2.9 1.92 3.81 4.7

Poraver (0.25–0.5 mm)

2.4 2.75 0.55 0.36 0.32

2.3 1.87 19 9 9

4.5 6.4 0.5 0.5 0.5

Poraver (1–2 mm)

Poraver (2–4 mm)

Sum of SS 1000

Gravel mix (GM)

Sieve analysis for normal weight coarse sand.

Sum of SS 2.27

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

Sieve analysis for normal weight gravel mix.

Table 5.

Table 4.

Specific gravity (ton/m<sup>3</sup> )

Moisture content

LWA and NWA properties.

Absorption capacity (%)

(%)

Table 6.

57

Sieve no. Weight retained (g) % retained % finer 5 0.5 99.5 49.5 5.45 94.55 283 33.75 66.25 286.5 62.4 37.6 364.5 98.85 1.15 11 99.95 0.05 pan 0.5 100 0

For CA = 1200 kg/m<sup>3</sup>

$$\mathbf{f}\_c = \mathbf{0}.\mathbf{0}\mathbf{6} \,\,\exp\left(\mathbf{1}.\mathbf{6}\mathbf{v}\right)\tag{5}$$

For CA = 1300 kg/m<sup>3</sup>

$$\mathbf{f\_c = 1.03 \,\exp\,(0.87v)}\tag{6}$$

For CA = 1400 kg/m<sup>3</sup>

$$\mathbf{f\_c = 1.39 \,\exp\,(0.78v)}\tag{7}$$

Table 3 showcases some of the different equations generated by researchers in the last decades to predict compressive strength of concrete, fc, in terms of UPV [15].

### 4. Experimental program

In this section an experimental program was developed and conducted by the author and his graduate student to investigate the compressive strength of LWAC containing a specific type of expanded glass aggregate (EGA), to better showcase the properties of LWAC [1].

#### 4.1 Lightweight and normal weight aggregates

#### 4.1.1 NWA

Tables 4 and 5 consist of the sieve analyses for the normal weight gravel and coarse sand, respectively, which were measured according to ASTM C136-01 [16].
