4.4 Results and discussion

In general it was observed that with increase in the amount of LWA in the concrete mixture, the compressive strength and UPV of LWC decrease, which was expected. In Figure 5, the relationship between UPV and fc (measured with ACM), at the age of 7 and 28 days for the LWC is presented. It can be observed that the results are scattered and more tests and specimens and concrete mixtures will be

Figure 4. Compression test machine.

Figure 5.

UPV versus fc for LWC tested at days 7 and 28.

required to be able to establish a solid relationship between UPV and compressive strength for this type of LWAC. The best empirical relation obtained from curve fitting analyses for this study can be written as below:

$$\mathbf{f\_c = 0.8 \,\exp\,(0.335v)}\tag{8}$$

where fc is the compressive strength of concrete (MPa) and v is the pulse

To be able to investigate the effect of the LWA content in the mix proportions, we have selected the mixes with constant w/c ratio of 0.47 and gradually replaced the NWA with LWA (Table 8). Figure 6 depicts the relation between fc and replacement ratio (RR) or LWA content for these individual mix proportions. From this figure, it can be observed that for the LWC in this study, as the LWA content increases, fc decreases. Figure 7 shows the relation between UPV and RR or LWA content for these individual mix proportions. From this figure, it can be observed that for the LWC in this study, as the LWA content increases, UPV decreases as

Mixes RR w/c Cement (g) Water (g) GM (g) CS (g) LWA, coarse (g) LWA, fine (g) 12a 0 0.47 576 272 3284 1275 — 0 12b 20 0.47 576 272 3284 1021 — 254 12c 40 0.47 576 272 3284 767 — 508 12d 60 0.47 576 272 3284 508 — 767 12e 80 0.47 576 272 3284 254 — 1021 12f 100 0.47 576 272 3284 0 — 1275

velocity (km/s).

UPV versus RR for LWC.

Figure 7.

Figure 6.

fc versus RR for LWC.

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

expected.

Table 8.

61

Comparison between different LWA contents.

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

where fc is the compressive strength of concrete (MPa) and v is the pulse velocity (km/s).

To be able to investigate the effect of the LWA content in the mix proportions, we have selected the mixes with constant w/c ratio of 0.47 and gradually replaced the NWA with LWA (Table 8). Figure 6 depicts the relation between fc and replacement ratio (RR) or LWA content for these individual mix proportions. From this figure, it can be observed that for the LWC in this study, as the LWA content increases, fc decreases. Figure 7 shows the relation between UPV and RR or LWA content for these individual mix proportions. From this figure, it can be observed that for the LWC in this study, as the LWA content increases, UPV decreases as expected.


#### Table 8.

Comparison between different LWA contents.

required to be able to establish a solid relationship between UPV and compressive strength for this type of LWAC. The best empirical relation obtained from curve

f <sup>c</sup> ¼ 0:8 exp 0ð Þ :335v (8)

fitting analyses for this study can be written as below:

UPV versus fc for LWC tested at days 7 and 28.

Figure 4.

Figure 5.

60

Compression test machine.

Compressive Strength of Concrete

#### Compressive Strength of Concrete

The relationship between UPV, fc (compressive strength), and dry density for the mix proportions in Table 8 is presented in Figures 8 and 9. It can be observed that for the LWC in this study, as the dry density increases, UPV and fc also increase, but the results are scattered when working with LWC. To be able to compare these results from those of NWC, mixes of NWC with similar compositions but without any LWA were produced, and results were presented in Figures 10 and 11. It is observed that the result for the relationship between UPV, fc and, dry density for LWC is more scattered than similar test result for NWC.

5. Conclusions

UPV versus dry density for NWC.

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

Figure 11.

63

There are different types of LWC available in the industry that depending on the method which is used for production of each type, the properties of the LWC can be completely different. Lightweight aggregate concrete (LWAC), foamed concrete (FC), and autoclaved aerated concrete (AAC) are among the most common types. On the other hand, structural and nonstructural lightweight concrete can be produced for different purposes. Lightweight aggregate concrete, such as the one discussed in this study, are being used nowadays in the advancement of concrete technology, but it is proven that each type of LWA needs to be tested before being used in structures and even for nonstructural purposes. Compressive strength of LWC is an important characteristic of LWC that can be measured or predicted with few methods such as NDT methods. Ultrasonic pulse velocity was utilized to assess the compressive strength, fc, of the LWC containing EGA in the present study. In this chapter it was observed that LWA can replace NWA to achieve smaller bulk densities and UPV can be used as a method for evaluation of compressive strength of LWC. Based on the case study conducted in the present chapter, it was showcased that as the dry density of the LWC decreased, UPV and fc decreased, respectively. Comparisons of actual fc values obtained from CTM proved UPV can be related to fc, and the results showed similar characteristics to previous works, while the previous work's equations cannot be used for the aggregates used in this study. The results of the present study are limited to the mix design and materials that were used in this work, and it should be noted that these results cannot be extended

to other types, sizes, etc. of aggregates and different mix designs.

Figure 8. fc versus dry density for LWC.

Figure 9. UPV versus dry density for LWC.

Figure 10. fc versus dry density for NWCUPV versus dry density for NWC.

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

Figure 11. UPV versus dry density for NWC.
