https://doi.org/10.14311/APP.2022.33.0271 Acta Polytechnica CTU Proceedings 33:271–276, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague STUDY FOR RE-ASR BEHAVIOUR OF RECYCLED CONCRETE USING ASR GENERATED CONCRETE AND CONSIDERING COUNTERMEASURE TECHNOLOGY Takeshi Iyodaa,∗, Nobuhiro Matsudab a Shibaura Institute of Technology, 3-7-5 Toyosu Koto-ku, Tokyo, Japan b Tokyo Techno Company, 3343 Onoji-machi Machida city, Tokyo, Japan ∗ corresponding author: iyoda@shibaura-it.ac.jp Abstract. It is predicted that the concrete volume to be discarded will increase due to the renewal of the concrete structures and the increase in the returned concrete from construction site. The use of this concrete block as recycled aggregate is very important in terms of sustainability. However, recycled aggregate concrete is difficult to use due to large problems such as drying shrinkage and freeze-thaw action. On the other hand, the aggregate used for the raw concrete is often unknown, suggesting the danger of ASR. There is no previous research about what kind of danger is caused when an aggregate having an ASR risk is used as a recycled aggregate. Therefore, in this study, recycled aggregate was made from raw concrete where ASR occurred, after that recycled concrete was manufactured using this aggregate. After this, ASR tests were conducted again for the recycled concrete. In addition, we examined whether recycled concrete using aggregates with properties improved by using the previously reported carbonation technique could be an ASR countermeasure technology. As a result, it was found that the recycled concrete using the ASR-generated raw concrete as aggregate can suppress ASR by using recurring ASR aggregate treated by carbonation technology. Keywords: Carbonation technology, re-ASR behavior, recycled concrete. 1. Introduction It is predicted that the concrete volume to be dis- carded will increase due to the renewal of the con- crete structures and the increase in the returned con- crete from construction site. It is important to use the recycled aggregate from this concrete to achieve sustainability society. Further, in order to spread re- cycled aggregate concrete, it is desired to use low- quality recycled aggregate that also generates few by- products such as fine powder and can be manufac- tured reducing energy and cost. However, recycled aggregate concrete has significant problems such as low strength, drying shrinkage and freeze-thaw. Fur- thermore, the recycled aggregate reactiveness is of- ten unknown for the danger of alkali-silica reaction (ASR). It should be noted that in ASR, alkali supply from attached mortar on recycled aggregate is also assumed. There has been little discussion about the dangers that would occur if concrete with reactive aggregates were used as recycled aggregate. In order to promote the use of low-quality recycled aggregate in the future, it is necessary to get more knowledge about ASR. On the other hand, in past works, the authors have proposed a modification technique by carbonation for the purpose of improve low-quality recycled aggregate [1–4]. This technology focuses on the carbonation mechanism of concrete, it applies high-concentration carbon dioxide on the recycled aggregate to carbonate the mortar in the recycled aggregate, thereby modi- fying the recycled aggregate itself. It has been con- firmed that recycled aggregate modified by this tech- nique meliorate concrete strength, length change by drying shrinkage and freeze-thaw resistance. How- ever, the impact on ASR has not been studied. Car- bonation was expected to have the effect of lower- ing the alkali concentration of the mortar, and was thought to be helpful in suppressing ASR. Therefore, in this study, the raw concrete was pre- pared by using the reactive coarse aggregate in or- der to develop ASR. The recycled coarse aggregate was manufactured from this raw concrete with con- firmed ASR, and the recycled concrete was prepared. At that time, recycled coarse aggregates low (L) and high (H) quality were produced. The recidivism of ASR (re-ASR) of this recycled concrete were experi- mentally investigated. In addition, the effect of ASR suppression using modified recycled aggregate by car- bonation was also investigated. 2. Outline of the experiments 2.1. Preparation of raw concrete and ASR characteristics Table 1 shows the types and physical properties of the aggregates. Regarding the rock types of each coarse aggregate, OG is crushed hard sandstone, KG is an- desite, and SG is gravel. The ASR characteristics of the aggregate used were confirmed by the chemical method (JIS A 1145), the mortar bar method (JIS A 1146) and the accelerated mortar bar method (ASTM 271 https://doi.org/10.14311/APP.2022.33.0271 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en Takeshi Iyoda, Nobuhiro Matsuda Acta Polytechnica CTU Proceedings Kinds Dry density Water absorption ration F.M. Sc Rc Classify of ASR! g/cm3" [%] [mol/l] [mol/l] OS Fine Agg. 2.55 2.18 2.82 28 84 Harmless OG Coarse Agg. 2.63 0.89 6.62 40 78 Harmless KG 2.72 1.72 6.41 388 94 Not harmless SG 2.60 1.18 7.41 73 107 Harmless Table 1. The types and physical properties of the aggregate. Figure 1. Mortar bar test on JIS. C 1567). The test results of the chemical method are shown in Table 1. The OS (fine aggregate), OG and SG were judged as "harmless" and KG was judged as "not harmless". Figure 1 shows the results of the mortar bar test using JIS. All the coarse aggregates were judged to be "harmless" with less than 0.1% of expansion ratio at the age of 26 weeks. However, for KG, the expansion increased after 13 weeks of age, and it is estimated that the expansion further increased after 26 weeks. Figure 2 shows the results of the accelerated mortar bar test by ASTM. The KG and SG were judged "harmful", and OG was "harm- less". It can be seen that the expansion amount of KG greatly exceeds 0.2% at 14 days of age, and the reactivity is high. The SG gradually expanded from around 5 days of age and exceeded 0.2% at 14 days of age, indicating that it is an aggregate with low to moderate reactivity. Based on the above results, KG and SG were determined to be reactive aggregates, and OG was determined to be harmless aggregates. Using these aggregates, raw concrete was produced with the planned composition shown in the Table 2. The cement used was ordinary Portland cement with a Na2O equivalent of 0.57%. In order to promote ASR, NaOH was added during mixing so the amount of alkali in concrete increased to 7.0 kg/m3. Ta- ble 2 also shows the fresh properties of the raw con- crete and the compressive strength when cured in tap water for 28 days. Regarding the fresh properties and compressive strength of the raw concrete, there Figure 2. Accelerated mortar bar test on ASTM. was no significant difference between the slumps, al- though it varied slightly. However, the compressive strength was slightly lower due to on the effect of adding NaOH. Next, a RILEM AAR-3 (38◦C con- crete prism test) test was performed to evaluate on the ASR characteristics of the raw concrete. Figure 3 shows the results of the RILEM AAR-3 test. The cri- teria for RILEM AAR-3 is described as those samples with a swelling above 0.04% at the age of 52 weeks are judged to be harmful. The KG aggregate concrete (KC) increases the swelling from around 10 weeks of age and 0.04% at the age of 52 weeks. Cracks were confirmed at 14 weeks. The swelling of SC gradu- ally increased around 10 weeks, and slightly exceeded 0.04% at 52 weeks. On the other hand, OC was deter- mined to be "harmless." These results show the same tendency as the ASR characteristics of the raw ag- gregate on the accelerated mortar bar test as ASTM. In order to prepare recycled coarse aggregate, cylindrical specimens of ! 100 × 200 mm were pre- pared. The raw concrete specimens were stored in an outdoor environment for one to three weeks to fur- ther promote ASR, and then cured in water at 40◦C. To check the amount of expansion of the raw concrete specimen, a 100×100×400 mm prismatic sample was prepared. Figure 4 shows the amount of expansion of the monitored specimens. The swelling behaviour of these samples were slower when compared with RILEM AAR-3 test. This is because the monitoring specimens were cured under the same conditions as 272 vol. 33/2022 re-ASR Behaviour of Recycled Concrete Kinds of Unit weight Fresh concrete properties Compressive Coarse agg. W/C C W S G Slump Air Temp. Strength [%] [kg/m3] [cm] [%] [◦C] [N/mm2] OC OG 981 11.0 4.7 25.0 29.4 KC KG 50 350 165 823 1021 6.5 4.3 24.0 28.7 SC SG 962 16.0 4.1 23.0 27.9 Table 2. Mix proportion, fresh properties and compressive strength of concrete at 28 days. Figure 3. ASR expansion test on RILEM. the concrete specimens. However, the amount of ex- pansion of KC increased rapidly from the age of 13 weeks, showing a similar tendency to the raw aggre- gate and raw concrete. At 20 weeks of age, cracks were confirmed in the test specimen. On the other hand, in SC, although the amount of expansion was slightly small, there was no significant difference from the expansion behaviour in the RILEM AAR-3 test. Recycling of the original concrete specimens was per- formed at about 20 weeks for KC and 26 weeks for OC and SC at the age of the monitoring specimens. 2.2. Production of recycled coarse aggregate Recycled coarse aggregates L and H and modified recycled aggregate LC were produced from OC, KC and SC raw concrete specimens. At this point, KC has confirmed expansion and cracking due to ASR. Recycled coarse aggregate L was produced only by crushing treatment (jaw crusher / impact crusher). Recycled coarse aggregate H was produced by further grinding (ball milling) the recycled coarse aggregate L. In the modified recycled aggregate, the coarse ag- gregate L was carbonated. The forced carbonation condition was 1 week long under the of temperature of 20◦C and relative humidity of 60% in the acceler- ated carbonation chamber, as in the previous study [1, 3]. All the produced recycled coarse aggregates were washed with water to remove fine particles. Fig- ure 5 shows the density and water absorption of the recycled coarse aggregate. In all types of modified recycled aggregate, the density and water absorption Figure 4. Expansion test on monitoring specimens. Figure 5. Density and water absorption ratio on recycled aggregates. properties had improved. There are also improve- ments for the quality of recycled coarse aggregate M. Although the alkali content was separately measured, no significant difference was found in the total alkali content of the recycled coarse aggregates L and H in this study. 3. ASR characteristics of recycled aggregate concrete 3.1. Outline of the experiment Concrete was prepared using the recycled coarse ag- gregate shown in Table 3 and the ASR characteris- tics were confirmed. The materials used the same as preparing recycled aggregate concrete. The composi- tion of recycled aggregate concrete was W/C = 0.5, 273 Takeshi Iyoda, Nobuhiro Matsuda Acta Polytechnica CTU Proceedings Kinds of Concrete Coarse agg. Compressive strength coarse agg. Non-NaOH Adding NaOH OL OC OG 37.1 24.2 OLC 38.5 27.5 OH 37.1 38.5 KL KC KG 39.3 25.5 KLC 40.3 30.7 KH 40.1 27.3 SL SC SG 35.8 24.5 SLC 38.5 26.7 SH 39.9 27.8 Table 3. Results of compressive strength on different concrete. s/a = 0.46, and unit water volume of 165 kg/m3. For the purpose of promoting ASR, two types were pre- pared, one with NaOH added and one without NaOH, so that the total alkali content in recycled aggregate concrete including alkali from cement was 7 kg/m3. In addition, the calculation of the total alkali con- tent of the sample to which NaOH was added did not include the alkali content from the aggregate. A 100 × 100 × 400 mm prism was prepared, and after demolding, it was cured for 1 week in an environ- ment at a temperature of 20◦C and humidity of 60%. Table 3 shows also the compressive strength on re- cycled concrete. The compressive strength tends to be larger for H class aggregate. It can be said that the amount of attached mortar affects the strength development. Also, the modified recycled aggregate has increased compressive strength compared to L, as in previous studies [2, 4]. When NaOH was added, the compressive strength was reduced. 3.2. Experimental Results Figure 6 shows the expansion of recycled aggre- gate concrete. Comparing the types of raw aggre- gates, those using the non-reactive raw aggregate OG showed almost no expansion regardless of whether NaOH was added or not. It is clear that there is no danger of ASR occurring again when recycled coarse aggregate made from non-reactive raw aggregate is used. In the case of using highly reactive KG, the amount of expansion was significantly increased with the addition of NaOH. Silica remains at the time of production of recycled coarse aggregate, and it is con- sidered that ASR occurred when recycled aggregate concrete was used. In addition, those without ad- dition of NaOH showed almost no swelling. This is probably because the total alkali content of recy- cled aggregate concrete using KG and not containing NaOH was 2.9 kg/m3, indicating that the alkali con- tent did not reach ASR. On the other hand, when SG was used, the aggregate had low to moderate re- activity as the ASR characteristics of the original ag- gregate, but almost no expansion was observed as in OG. Comparing L and H, H increased the rate of expan- sion when NaOH was added and using reactive ag- gregate. This is considered to be due to the fact that the amount of attached mortar with H was small, so that the elution of silica and the penetration of alkali were easily performed. On the other hand, in the case of using KG with high reactivity without addition of NaOH, L slightly expanded. It is possible that the al- kali in the attached mortar affects ASR. In addition, the amount of expansion is greatly suppressed by us- ing the modified recycled aggregate. In particular, those using highly reactive KG as the raw aggregate were very remarkable, showing a high suppression ef- fect on ASR. Figure 7 shows an image of this ASR suppression mechanism. In addition to the presence of attached mortar, the modified recycled aggregate become denser by carbonation, which suppresses the penetration of alkali and further dissolution of silica in the raw aggregate. It is thought that ASR is re- duced by suppressing it. However, in this experiment, the expansion of the original concrete due to ASR was considered to have calmed down to a certain extent, and the scope of the experiment was limited. In the future, it is necessary to continue studying the raw concrete before ASR progresses, and also to confirm the suppression mechanism by the modified recycled aggregate. 4. Summary The following findings were obtained in this study. 1. The ASR characteristics by the accelerated mortar bar method in raw aggregate and RILEM AAR-3 in raw concrete showed the same tendency. 2. It was found that there was no danger of ASR oc- curring again when recycled coarse aggregate made from non-reactive raw aggregate was used. In the case of using highly reactive KG, the amount of expansion significantly increased with the addition of NaOH. This suggests that even when the ASR of the raw aggregate has progressed to some ex- tent, the silica remains when the recycled coarse 274 vol. 33/2022 re-ASR Behaviour of Recycled Concrete Figure 6. Results of re-ASR on recycled concrete. Figure 7. The mechanism of prevented ASR on using carbonated recycled aggregate. 275 Takeshi Iyoda, Nobuhiro Matsuda Acta Polytechnica CTU Proceedings aggregate is made, and when the recycled aggre- gate concrete is used, the ASR occurs again. 3. When L and H quality recycled aggregate were compared, the expansion was higher for H with the addition of NaOH and using reactive aggregate. 4. The swelling behaviour was greatly suppressed by using the recycled aggregate modified by carbon- ation, and for the one using highly reactive KG as the original aggregate the decrease was very re- markable, showing a high inhibitory effect on ASR. Acknowledgements This experiments were carried out by Mr. ABDULKA- REEM ABDULKADEER ABDULLAHI and the all members of our laboratory. References [1] N. Matsuda, T. Kameyama, M. Matsuda, et al. Study on the Production Method of Low-Energy Recycled Aggregate by Forced Adsorption of CO2 Gas. Proceedings of the Japan Concrete Institute Annual Convention 36:1732-1737, 2014. [2] N. Matsuda, S. Suzuki, T. Iyoda. Proceedings of the Japan Concrete Institute Annual Convention 38:1791-1796, 2016. [3] T. Iyoda, N. Matsuda. II International Conference on Concrete Sustainability, pp. 132-141, 2016. [4] A. A. Abdulkadeer, N. Matsuda, T. Iyoda. IALCCE2018 The Sixth International Symposium on Life-Cycle Civil Engineering, pp. 575-582, 2018. 276