Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016
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- 2.2 Mechanical strength test
- 2.3 Discussion of results
399 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
Compressive strength testing was undertaken at 7 and 28 curing days for all mixtures following the standard procedure in NP EN 196-1 [28]. Results are presented in Figure 2.
Figure 2 - Compressive strength results.
The autogenous shrinkage of UHPC mixtures was measured based on the ASTM C1698 [29], in which three sealed corrugated moulds of 440 mm length and 28.5 mm average diameter were filled for each mix composition. After filling the tubes, each specimen was measured and weighted, and kept inside a chamber with controlled temperature (23±1°C) (see Figure 3). Shrinkage deformations were recorded continuously using DC LVDT and a dataTaker DT500 acquisition system. According to this standard, the length change of samples should be evaluated starting at the time of final setting of the mixture. Final setting time test was carried out on the UHPC mixtures adapting the procedure of section 6.3 of standard EN 196-3 [26]. After 7 days, each specimen was weighted again and mass change was recorded in order to validate the test [29]. Figure 4 shows the development of autogenous shrinkage of REF and SF UHPC mixtures and Figure 5 presents autogenous shrinkage of mixtures incorporating different amounts of ECat. Each curve corresponds to an average of the length change of three specimens tested for each mixture. Table 2 presents the autogenous shrinkage results at 24 hours and at 7 days along with the corresponding the mass variation, as well as the corresponding predicted values according to Japan Society of Civil Engineers (JSCE) [30].
Figure 3 – Experimental setup for autogenous shrinkage testing. 0.00 20.00
40.00 60.00
80.00 100.00
120.00 140.00
REF SF SF+Ecat10 SF+Ecat20 SF+Ecat30 SF+Ecat40 (MPa)
UHPC Mixtures 7 dias
28 dias 400 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
Table 2 - Autogenous shrinkage (between brackets the standard deviation) and mass variation results at 7 days. Mixture
REF SF SF+ECat10 SF+ECat20 SF+ECat30 SF+ECat40 Autogenous Shrinkage at 24h ( m/m) 873(±2%) 989(±3%) 843(±3%) 607(±8%) 664(±5%) 1201(±5%) Autogenous Shrinkage at 7 days ( m/m) 959(±1%) 1118(±3%) 881(±3%) 687(±6%) 750(±6%) 1305(±5%) Mass Variation (%) -0.04 -0.17
0.01 0.00
0.00 0.00
JSCE autogenous shrinkage prediction ( m/m) at 7 days [30]
778
Figure 4 - Autogenous shrinkage of REF and SF mixtures.
0
400 600
800 1000
1200 1400
0 24 48 72 96 120 144 168
( m/m)
Time after final setting (hours) SF REF 401 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
Regarding fresh state of UHPC mixtures, ECat influenced the flow ability of mixtures (Table 1). Up to 20% replacement level of sand with ECat the effect on Dflow was negligible, however for higher amounts Dflow decreased substantially, needing extra superplasticizer dosage, corroborating the findings of previous studies [12], [22], [31], [32]. In general, the higher the sand replacement percentage by ECat, the shorter the setting times. The results of the mechanical properties (Figure 2) show that on the 7-day curing the compressive strength of the SF mortar is already slightly higher than that of plain cement mortar (REF) and that this difference increased at 28-days curing. These compressive strength improvement, since early age, is attributed to the relevant pozzolanic reactivity of SF. Furthermore, mortars with partial sand replacement with ECat up to 30% also show a strength-enhanced slightly higher than those of the REF and SF mortars. These results are due to the fact that besides the binder, these mortars contain the ECat generated in the Portuguese refinery that also possess high early pozzolanic activity of [22], [23] which forms additional strength-providing reaction products, C-A/S-H, that promotes the mechanical properties improvement too. However, both at 7 and 28 curing days, mortars show an approximately linear decrease in the compressive strengths with the increase of the ECat incorporation level. This trend may be attributed to changes in the particle size distribution of the sand-ECat mixtures (Figure 1) that may lead to a decrease in their packing ability and, therefore, compromising the strength development. In fact, this phenomenon can also explain the need of extra superplasticizer in the mortars with higher level of sand replacement with ECat. The autogenous shrinkage of all UHPC mixtures exhibited a strong increase during the first hours from the final setting, particularly in the first six hours, and then increased but with a lower rate (Figure 5). SF mixture presented a higher autogenous shrinkage than REF mixture, as expected. Previous studies showed that no Relative Humidity change was linked to the silica fume pozzolanic reaction during which CH-crystals were consumed and explained the additional shrinkage as chemical shrinkage that markedly increases autogenous shrinkage compared with mixtures with Portland cement only. The finer pore structure of the cement
Figure 5 - Autogenous shrinkage of REF, SF and SF+ECat mixtures. 0 200 400 600
800 1000
1200 1400
0 24 48 72 96 120 144 168
( m/m)
Time after final setting (hours) SF+ECat40 SF SF+ECat10 SF+ECat30 SF+ECat20 Yüklə 8,6 Mb. Dostları ilə paylaş:
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