4 ms·

Hand-held devices for testing concrete properties would be more useful. Most concrete problems come from a bad mix - too much water, not enough cement, etc. Con

• harimau777 7mo ago
  I'm surprised the ratios for a given situation isn't standardized by now. Is it just people cutting corners?
  • Aurornis 7mo ago
    Working with multiple tons of material that dries out as you move it around is hard. There are a lot of steps between the concrete being mixed and when it finally reaches the pour. Cutting out a piece of a slab and sending it to a lab is for post-pour validation in serious construction. There are pre-pour tests that are much simpler depending on the seriousness of what you’re building. The slump test is rather simple, for example: https://en.wikipedia.org/wiki/Concrete_slump_test https://en.wikipedia.org/wiki/Concrete_slump_test It’s basically a cone with handles and a procedure that’s easy to learn.
  • m4rkuskk 7mo ago
    They are standardized for a given mix. A mix design that is based on a trial badge is submitted to the SEOR prior to pouring anything. The mix design shows the ratios ingredients (cementitious materials, find and coarse aggregates, water, air, admixtures). But Concrete is still a non-homogeneous material with lots of variations. Take for instance aggregates, if it rained the last two weeks, the moisture content will be higher but it may only be a layer on that pile. Same goes for gradation (particle size of the rock). Sometimes you get a batch with smaller rock. There are a 100 things that can go wrong to get bad mud. But yeah, there are concrete plants that cut corners and try to save on cement (the most expensive part of the mix), which depending on the project may bite them in the ass when they have to pay to fixing it.
  • themafia 7mo ago
    When you're making tons of something process variations get magnified.
  • munk-a 7mo ago
    No - it's actually local variance in materials coupled with the difficulty in moving materials between markets economically. Some areas just have better suited limestone or gravel or sand and can afford to build resilient structures for a fraction of the price that it'd cost in other areas. This issue here is mainly that it's very expensive to ship all the components of a Concrete in the volume necessary in an economical manner. Some areas of the world just lost the lottery when it comes to having resilient building materials. Corruption absolutely is an issue as well - I don't mean to downplay it - but even if we remove it as a factor there are just a lot of variables involved in making a reliable Concrete... finding a good mix is an artform and if, for instance, your limestone quary suddenly hits a more clay-laden amalgamation then your Concrete that was reliably lasting for three decades under certain conditions might suddenly lose a decade off the expected lifetime. That change in material quality can also be difficult to detect so there are real quality assurance issues in Concrete mixtures outside of just corruption and cutting corners.
  • bluGill 7mo ago
    My grandpa used to be a concrete inspector (for the state of Minnesota - if you ever drive i394 there he was one of the inspectors for that). Different plants within a normal commute of his house often had very different sand and so needed a different mix.
    • quickthrowman 7mo ago
      Oh cool, did he work for MNDOT? I sell and run a lot of work at their facilities, they have a materials lab over in Maplewood off Hwy 36 and English St, and also the weird test surface area on 94 west of St Cloud.
      • bluGill 7mo ago
        Yes, drove snow plows in the winter from Chaska (no longed there). He retired long ago.
• MisterTea 7mo ago
  On-site, before pouring, they use the slump test: https://en.wikipedia.org/wiki/Concrete_slump_test https://en.wikipedia.org/wiki/Concrete_slump_test
  • sidewndr46 7mo ago
    Glad to see someone pointed this out. The test consists of a bucket, plywood board & a stopwatch.
    • jauntywundrkind 7mo ago
      Hopefully there's good empirical data powering the model here, which just added slump prediction: > Alongside the event, Meta is releasing a new AI model for designing concrete mixes, Bayesian Optimization for Concrete (BOxCrete). BOxCrete improves over Meta’s previous models with more robustness to noisy data as well as new features including the ability to predict concrete slump (an important indicator of concrete workability). Seems hard to imagine not doing a slump test, trusting AI when it comes to your multi/many million dollar build outs for something so important. But perhaps still useful for planning, as a starting place?
      • sebastianeament 7mo ago
        The predictions of the model are used as recommendations for onsite testing to accelerate finding mixtures with optimal strength-speed-sustainability trade-offs. We are not replacing canonical testing with the model.
      • bluGill 7mo ago
        There is a lot of expense in the wasted concrete from all the different pours that are slump tested. There is a lot of cost from concrete that leaves the plant only to fail slump testing when it gets there - not only do you have to empty the truck someplace else, but there maybe contract provisions if you fail to keep the workers busy. Often more than one test is done - if the plant has an order that they know will be tested they test before it leaves the plant (if it fails they can redirect to a different customer who will knowingly accept lesser concrete - but concrete cures on the truck so it would be unacceptable if rejected at the site to go elsewhere). Many smaller jobs skip the test, but they would like it done if it was free. That said, I'm not sure if the value can ever be greater than a slump test just before pouring.
• no_shadowban_6 7mo ago
  [flagged]
  • michaelmrose 7mo ago
    Do you actually see construction workers being replaced? We need more stuff built than we have people or time. We have spent a century improving process and tools and if we 10 years from now could build 3 times as much with the same people we would find a use for them all.
    • no_shadowban_6 7mo ago
      Quality is irrelvant these days. If AI does it cheaper, you're done.
      • mrhottakes 7mo ago
        How cheap are existing AI construction workers?
  • knicholes 7mo ago
    Yikes, what a flippant comment. The mix composition (meta's AI is helping with this) is separate from the wet concrete product. The parent is suggesting a way to test that the mix is properly mixed before pouring, not suggesting a way for construction workers to determine that the chemical properties of the mix will be correct on site. Furthermore, they're not even using LLMs, so it's not "AGI".
• munk-a 7mo ago
  > too much water, not enough cement, etc. I wanted to mention that Concrete is far more complex and regional than folks might imagine. The quality of gravel and sand, local impurities - these all contribute massively. It's probably best to think of it like a wine's terroir - except, unlike a bottle of wine, it's prohibitively expensive to ship both the components and the finalized mixture to different areas. If a region's limestone has a massive clay impurity then it may simply be unsuitable for large structures or require extensive filtering to the point of being uneconomical. It's important to be aware of just how much the local geological mix can impact the viability of building with concrete because while theoretically we could use perfect concrete for every project - at that point most projects would simply be too expensive to consider undertaking. There is a very large field of engineering around establishing the realism required in settling for what you've got for the price you can afford in. It can absolutely mean that the materials required to build a high rise in Philly might be priced starkly differently from the same structure planned in Milan even with adjustments for the labor impact on pricing.
  • bluGill 7mo ago
    > it's prohibitively expensive to ship both the components and the finalized mixture to different areas. We could do this if it is important. There are mines in Wisconsin the export sand to the middle east because that is known to work well for fracking and they don't want to risk a local sand not working well. (AFAIK they have never tested local sand properties, but it is possible they have and it doesn't work). In this case the value of the "perfect" is well worth the high shipping costs.
    • munk-a 7mo ago
      We certainly could - it's absolutely possible. The question is if it's economical and so far the market has ruled in most cases that it isn't. Either the project doesn't need such a perfect amalgamation of materials (maybe there is an expected deprecation that doesn't justify such an outlay - possibly earthquake risk would minimize any expected lifespan gain - possibly the materials contractor just can't internally justify the added material cost while remaining attractive to local contractors). It's all a balance. Imagine a scenario where you can ship in specialized materials to build a bridge with an expected lifespan of 100 years and it'll cost 50M - or you could use local concrete that has an expected lifespan of 15 years and materials would cost 5M. This is a vast simplification of the math but, assuming those expected costs it'd be cheaper to build using local materials and just schedule replacement every 15 years. And, of course, there'll be egg on your face if you build the 50M bridge and then suffer a massive tsunami in two years that destroys the foundations anyways. To paraphrase a Grady quote: "Engineering isn't a study of building the best thing - it's optimizing the quality we can get for the cost outlay."
• prpl 7mo ago
  I think people rarely reject even if it fails a slump test though
• GorbachevyChase 7mo ago
  It’s customary to prefix these comments with credentials, so I’ll just say that I’m a roadway engineer. Sampling at the batch plant or even at the truck is not going to give you the whole story. While the most common crime of contractors is to overwater the concrete slurry to make it flowable, other problems in workmanship can arise from failing to vibrate the concrete in its forms, leaving voids, or vibrating it too much, creating segregation of the aggregate. If the finisher overworks the concrete or tries to correct the shape when it’s green, the that can compromise strength. If the concrete is finished too early, you can get delamination. If time allows and your contractor is careful they might protect the freshly poured concrete and let it cure wet. That makes a huge difference in cracking. There is also a whole world of chemical additives that structural engineers don’t even think about in the design process. I’m not trying to say that mix doesn’t matter, or that I’m not pleased to see that Facebook is doing something a little more noble than surveillance technology, but as with a lot of construction issues, it’s just not that simple.
  • datsci_est_2015 7mo ago
    “it’s just not that simple” - my career in industrial data science in a nutshell. Lots of large companies come into the domains I’ve worked in with grand promises, and while sometimes they move the needle in terms of what executive leadership within the industry believes is possible, they also often poison the well for us smaller firms who provide much more leveled and concrete (heh) offerings. Curse IBM, for example.
    • mschuster91 7mo ago
      AI is just the same. CEOs all over the world have fallen to the lure of the AI grifters, believing they can fire people en masse now and ride it out with the remaining staff until AI catches up with the remaining 20% of capability. Small focused AI/ML companies however that don't deal in LLMs? They struggle to find customers, even with stuff that clearly works, because they hit the wrong buzzwords.
  • emmelaich 7mo ago
    Is the slump test still commonly used? https://en.wikipedia.org/wiki/Concrete_slump_test https://en.wikipedia.org/wiki/Concrete_slump_test