1 00:00:00,000 --> 00:00:05,000 (deep swooshing sound) (booming sound) 2 00:00:09,370 --> 00:00:11,910 - [Narrator] Years ago, micro cracks were discovered 3 00:00:11,910 --> 00:00:14,910 on the surfaces of unused bridge girders, 4 00:00:14,910 --> 00:00:18,610 located at the state's precast concrete plants. 5 00:00:18,610 --> 00:00:21,730 Those same cracks were also found on some of the bridges 6 00:00:21,730 --> 00:00:23,900 where the girders had been installed, 7 00:00:23,900 --> 00:00:24,920 but why? 8 00:00:24,920 --> 00:00:26,960 And could this lead to more cracking 9 00:00:26,960 --> 00:00:29,910 and shortened surface life of the bridges? 10 00:00:29,910 --> 00:00:31,770 - It didn't look like there was necessarily a pattern 11 00:00:31,770 --> 00:00:34,270 to when this cracking occurred and when it didn't. 12 00:00:34,270 --> 00:00:36,130 And so we looked at different seasons, 13 00:00:36,130 --> 00:00:38,010 we looked at time of day, we looked at temperatures, 14 00:00:38,010 --> 00:00:39,910 we looked anything you can imagine. 15 00:00:39,910 --> 00:00:40,960 Finally got to the point I was like, 16 00:00:40,960 --> 00:00:43,470 well, just looking and trying to figure out the pattern 17 00:00:43,470 --> 00:00:44,650 wasn't gonna resolve it. 18 00:00:44,650 --> 00:00:46,440 So we started needing to take some cores, 19 00:00:46,440 --> 00:00:49,000 get some, study what's exactly going on. 20 00:00:49,000 --> 00:00:51,560 - So one of the main questions we had is that 21 00:00:51,560 --> 00:00:54,060 we know if it just had a single micro crack 22 00:00:54,060 --> 00:00:56,250 that is not really going to cause an issue, 23 00:00:56,250 --> 00:00:58,270 but what happened when you have many cracks? 24 00:00:58,270 --> 00:01:00,200 So what is the effective crack density 25 00:01:00,200 --> 00:01:01,820 when you're looking at micro cracks? 26 00:01:01,820 --> 00:01:05,290 So we did the field studies in which we're monitoring 27 00:01:05,290 --> 00:01:07,430 in service girders over time. 28 00:01:07,430 --> 00:01:10,830 And then we also augmented that with some laboratory studies 29 00:01:10,830 --> 00:01:13,170 in which we cast concrete mixtures, 30 00:01:13,170 --> 00:01:16,070 we subjected those concrete specimen 31 00:01:16,070 --> 00:01:18,210 to accelerated weathering tests 32 00:01:18,210 --> 00:01:20,840 by subjecting it to moisture, 33 00:01:20,840 --> 00:01:23,850 as well as simulating a marine environment. 34 00:01:23,850 --> 00:01:27,080 And we developed a model to predict what, 35 00:01:27,080 --> 00:01:29,240 how these cracks would grow over time 36 00:01:29,240 --> 00:01:30,450 and more importantly, 37 00:01:30,450 --> 00:01:32,640 how they may impact the strength 38 00:01:32,640 --> 00:01:36,490 as well as the corrosion resistance of the concrete. 39 00:01:36,490 --> 00:01:37,870 - So if these cracks get deep enough 40 00:01:37,870 --> 00:01:40,440 or wide enough to allow water in and chlorides 41 00:01:40,440 --> 00:01:41,273 and things like that, 42 00:01:41,273 --> 00:01:42,630 and it gets to the reinforcing steel, 43 00:01:42,630 --> 00:01:44,180 that's gonna quickly deteriorate the bridge. 44 00:01:44,180 --> 00:01:46,400 And so, that's the biggest thing we're trying to avoid. 45 00:01:46,400 --> 00:01:50,050 - We found that depending on the nature of the micro cracks, 46 00:01:50,050 --> 00:01:52,010 that it could impact the surface life 47 00:01:52,010 --> 00:01:53,470 between 2 to 13 years. 48 00:01:53,470 --> 00:01:55,670 So that means a 2 to 13 year reduction 49 00:01:55,670 --> 00:01:59,430 in the overall service life of the bridges. 50 00:01:59,430 --> 00:02:02,020 So our major recommendation for TxDOT is that 51 00:02:02,020 --> 00:02:05,550 in terms of monitoring, additional monitoring is needed, 52 00:02:05,550 --> 00:02:08,939 particularly towards the very end of the service life 53 00:02:08,939 --> 00:02:10,010 of the bridges. 54 00:02:10,010 --> 00:02:11,780 - We believe the cause of the cracking 55 00:02:11,780 --> 00:02:13,620 was related to shrinkage. 56 00:02:13,620 --> 00:02:16,700 Now, why it's shrinking more than what it had prior 57 00:02:16,700 --> 00:02:17,880 to that period? 58 00:02:17,880 --> 00:02:19,150 We're not quite certain of that. 59 00:02:19,150 --> 00:02:21,050 We think it may have been coincidental 60 00:02:21,050 --> 00:02:24,150 with the big drought we had from 2010 to 2015, 61 00:02:24,150 --> 00:02:25,860 because towards the end of that sort of drought 62 00:02:25,860 --> 00:02:27,700 is when we started noticing some of this cracking. 63 00:02:27,700 --> 00:02:30,420 And so, you've believed that played a role 64 00:02:30,420 --> 00:02:31,253 the environment. 65 00:02:31,253 --> 00:02:33,120 In fact, what we should said, 66 00:02:33,120 --> 00:02:36,180 was environmental impact does play a significant role 67 00:02:36,180 --> 00:02:38,030 in how much cracking is going to occur. 68 00:02:38,030 --> 00:02:40,230 - We've already have really good specifications 69 00:02:40,230 --> 00:02:43,950 about how a single crack is going to impact strengthened, 70 00:02:43,950 --> 00:02:47,770 it's going to impact corrosion resistance. 71 00:02:47,770 --> 00:02:51,720 What we didn't know is how many small cracks 72 00:02:51,720 --> 00:02:52,700 are going to affect it. 73 00:02:52,700 --> 00:02:55,420 That's really where we had this gap in the research, 74 00:02:55,420 --> 00:02:56,700 the gap in the science. 75 00:02:56,700 --> 00:02:59,250 And what this project really showed is that, 76 00:02:59,250 --> 00:03:01,240 yes if you had one little micro crack, 77 00:03:01,240 --> 00:03:03,160 that's not going to make a difference, 78 00:03:03,160 --> 00:03:06,010 but if you do have many micro cracks, 79 00:03:06,010 --> 00:03:08,300 the density of those micro cracks 80 00:03:08,300 --> 00:03:10,800 can actually exacerbate the problem 81 00:03:10,800 --> 00:03:14,003 and impair long-term durability. 82 00:03:14,940 --> 00:03:16,110 - [Narrator] For more information, 83 00:03:16,110 --> 00:03:18,580 and to find the publications for this project, 84 00:03:18,580 --> 00:03:21,460 please visit the TxDOT Research Library 85 00:03:21,460 --> 00:03:22,993 at the link shown below.