Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

109

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

every 5 cycles. The damage caused by PSA was assessed by means of mass loss. The 

measurements were taken every 10 cycles. 

 

Fundamental transverse, longitudinal, and torsional resonant frequencies of mortar specimens 

was measured using forced resonance method according to ASTM C215 [17]. Ultrasonic 

pulse velocity was measured in accordance with ASTM C597 [18] using transducers with the 

resonant frequency of 54 kHz. Mass loss was measured using scales with the capacity of 3 kg 

and precision of 10 mg. 

 

 

3.  Results and discussion 

 

The deteriorated mortar samples after 100 thermal cycles are shown in Figure 1. As can be 

recognized in Figure 1, the nature of damage caused by PSA is surface scaling. It can be seen 

that tested mixtures exhibited degree of deterioration ranging from very high in mortar with 

w/b ratio of 0.50 to minor in the mortars with slag. However, besides the size change, it is 

very hard to rate the degree of deterioration by visual appearance. The surface of all samples 

was affected by PSA. If significantly larger samples would be used in testing, it would be 

hard to quantify visually the difference between the resistance to PSA of these mixtures. For 

this reason, the rate of deterioration due to PSA was also assessed using mass loss, dynamic 

modulus of elasticity by measured by means of UPV, fundamental transverse frequency and 

fundamental longitudinal frequency, and modulus of rigidity determined by fundamental 

torsional frequency. The comparison of the mass loss and the durability factors determined by 

these methods for mortar with w/b ratio of 0.50 is shown in Figure 2. 

 

 

  

Figure 1: Deteriorated samples after 100 thermal cycles 

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110

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

        

 

Figure 2: Comparison of different methods for evaluation of deterioration rate for mortar with 

w/b ratio of 0.50. 

 

 

Figure 3: Durability factor based on fundamental transverse frequency 

 

The mortar with w/b ratio of 0.50 was selected to show the differences between various 

methods used to assess the rate of PSA, because it had the highest degree of damage, although 

the same tendency was observed in all tested mortar mixtures. It can be seen in Figure 2 that 

only mass loss reflects the full extent of degradation caused by PSA. It should be noted that 

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111

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

durability factor based on a fundamental frequency may be calculate by different ways. For 

example, in ASTM C666 [19], durability factor is calculated based on the ratio of the square 

of the fundamental frequency after and before the detrimental exposure. However, dynamic 

properties depend not only on the fundamental frequency, but on the mass and dimensions of 

the tested sample. In case of severe damage, mass loss and dimensional changes may 

significantly affect the fundamental frequency. In Figure 3, the durability factor is calculated 

based on the fundamental transverse frequency only, with corrections for mass and with full 

correction for mass loss and dimensional changes are compared. As can be seen in Figure 3, 

the reduction of dynamic transverse modulus of elasticity is about 20%, while durability 

factor based solely on the fundamental frequency reduces by more than 50%. Because of high 

mass loss, the durability factor with the correction for the mass shows degradation of almost 

90%. However, as can be seen in Figures 2 and 3, due to the nature of damage the true elastic 

properties of the mortar exposed to PSA are not impaired proportionally to the extent of 

deterioration. Figure 3 shows the values calculated based on fundamental transverse 

frequency as it is the most widely used method, but the same pattern appears in the other 

dynamic properties. In addition, due to significant reduction of the cross-section, the 

dimensional ratio of length to maximum transverse direction is shifted away from the 

optimum. Thus, it may be concluded that mass loss is the most effective approach to 

evaluation of the damage in PSA. 

 

The comparison of mortar mass losses during PSA exposure is given in Figure 4. Here the 

difference in PSA resistance between various mixtures can by quantified more easily than by 

visual appearance. In addition, it can be recognized that the rate of deterioration during PSA 

exposure was not constant. The rate of mass loss of mortars as function of thermal cycles 

number is shown in Figure 5. It can be seen that all mixtures demonstrated a sort of induction 

period in the beginning of exposure. Most mixtures increased the mass during the first 10 

cycles, after which the mass loss started with an increasing rate. After this initial period the 

rate of mass loss either stabilized or decreased. There may be two reasons for the decrease of 

the rate of mass loss. First, the size of deteriorating specimens decreased, and the surface 

available for PSA is reduced as well. Since the nature of the damage causing mass loss is 

surface scaling, the rate of mass loss depends on the surface area exposed to PSA. Second, the 

specimens during PSA exposure are submerged in sodium sulfate solution. This may promote 

hydration, particularly in the mixtures containing SCMs. Most probably, this is the reason for 

the reduction of the rate of mass loss in the mixtures with fly ash as the later stages of testing. 

Thus, FA mixtures could benefit from a longer period of moist curing. Further investigation is 

needed to confirm this hypothesis. 

 

As expected, the reduction of w/b ratio increases the resistance of mortars to PSSA. The 

difference in PSSA resistance between w/b ratios of 0.50, 0.45 and 0.40 are significant. 

However, there is not much change in PSA resistance between w/b ratio of 0.40 and 0.35. The 

possible reasons for this behavior maybe insufficient compaction, since the workability of 

mortars decreased with w/b ratio since no plasticizing admixture was used. Comparing the 

resistance of mortars with and without SCMs with the same w/b ratio, it can be seen that 

GGBFS significantly improved the resistance to PSA, while it was reduced with FA. It is 

interesting to note that the content of SCMs didn’t have significant impact on the behavior of 

mortars in PSA. 

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