Relationship between ultrasonic velocity and compressive strength for high-volume mineral-admixtured concrete
Introduction
At present, the investigation of nondestructive testing techniques [1] is a very popular subject. The ultrasonic method [2], [3] is one of the nondestructive testing techniques and is frequently adopted for evaluating the quality of in situ concrete structures.
The ultrasonic pulse velocity (UPV) technique is used as a means of quality control of products which are supposed to be made of similar concrete: both lack of compaction and a change in the water/cement ratio would be easily detected. The technique cannot, however, be employed for the determination of strength of concretes made of different materials in unknown proportions [4]. It is true that there is a broad tendency for concrete of higher density to have a higher strength (provided the specific gravity of the aggregate is constant) so that a general classification of the quality of concrete on the basis of the pulse velocity is possible [5]. Some figures suggested by Whitehurst [6] for concrete with a density of approximately 2400 kg/m3 are given as excellent, good, doubtful, poor and very poor for 4500 m/s and above, 3500–4500, 3000–3500, 2000–3000 and 2000 m/s and below UPV values, respectively. According to Jones and Gatfield [5], however, the lower limit for good quality concrete is between 4100 and 4700 m/s.
The measurement of the ultrasonic compressional wave velocity has been used for a long time to evaluate the setting and hardening of cementation systems [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].
Admixtures, such as fly ash (FA) and blast furnace slag (BFS), are used as replacement for cement for improving the mechanical properties, decreasing the rate of hydration, decreasing the alkali aggregate reactivity and decreasing the permeability of concrete. However, their effects on the ultrasound and the relationship between compressive strength and UPV have received little attention.
The relative performance of the FAs in concrete depends on the brand of cement used. In addition, the age of the test is an important factor influencing the relative performance of the various cementing materials [17].
Due to the rapid economic development and the growth in the world population consumption of the energy over the world, the FA has significantly increased. Thus, air and environmental pollution became a problem, then; the idea of using waste material has gained popularity. FA and BFS are the most common concrete ingredients due to their pozzolanic properties [18], [19].
There are many studies related to the UPV; for example, Tharmaratnam and Tan [20] provided the empirical formula of the combined UPV and ultrasonic pulse amplitude (UPA). Liang and Wu [21] studied theoretical elucidation of the empirical formulae for the UPV and UPA and combined methods. Ye et al. [22] determined the development of the microstructure in cement-based materials by means of numerical simulation and UPV. However, the relationship between the UPV and compressive strength of mineral-admixtured concrete has not been investigated. This study focused on the relationship between compressive strength of mineral-admixtured concrete and UPV.
Section snippets
Experimental study
ASTM Type I [23] Portland cement (PC) from Set cement factory in Ankara, Turkey was used in this study. FA, BFS and aggregate were obtained from Afşin Thermal Power Plant, İskenderun Iron-Steel Factory in Hatay-İskenderun and Aras River in Erzurum in Turkey, respectively. The chemical composition and physical properties of the mineral admixtures used in this study are summarized in Table 1.
Zero percent, 50%, 60% and 70% FA or BFS were used in replacement of PC. In addition, 25% FA+25% BFS, 30%
Results and discussions
The results obtained in the tests are shown in Table 3 and Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11. They are evaluated and discussed below.
Conclusions
- 1.
High-volume FA replacement induced to reduction in compressive strength at all levels of replacement. The gap in the compressive strength was very high at early age, but with increasing curing period, the gap decreased. UPV values also increased with the increasing curing period for FA samples. Maximum reductions occurred for 70% replacement of FA.
- 2.
The maximum compressive strength and UPV were observed with the control samples. Both compressive strength and UPV were very low for all levels of
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