I dunno....that's why I'm asking for input...
Below is the article, which shows the harmful effects of rain to freshly finished concrete. This is why I'm wondering why despite the information below, they still pour concrete on the construction project while its still raining...
http://www.cement.org/tech/faq_rain.asp
Frequently Asked Questions
Cement & Concrete Technology Home > FAQs > Rain on fresh concrete
Q: How does rain affect fresh concrete?
A contractor placed a concrete driveway for me last night. Before they could start the finishing work, it rained for several minutes. We covered everything we could but the concrete still got quite wet. In the end, they were able to finish (floating and edging), but I am really concerned how this will hold up long term.
A:Rainfall during placement of concrete flatwork can present challenges to achieving a quality concrete. Potential outcomes range from no damage to a weakened nondurable surface. Only time will tell at which end of the range your specific situation will fall. Descriptions of a best case scenario and a worst case scenario follow:
Plastic sheets used to protect the freshly placed concrete from rain.
Best case: The concrete is protected as much as possible from the falling rain. After the rain has stopped, the water that has fallen on the surface is allowed to evaporate just as bleed water from the original concrete mixture must be allowed to evaporate prior to proceeding with finishing operations. To substantially change the water-cement ratio (w/c) of the concrete at the surface of the slab, energy must be added to the system, typically in the form of troweling passes with excess water on the concrete surface. If the water is allowed to evaporate, the w/c remains reasonably low, and since w/c governs the strength of the concrete there is no substantial damage to the finished surface. In extreme cases it is not uncommon to physically remove excess water from the slab surface by dragging a garden hose or a broom across the concrete surface to lower the volume of water that must evaporate. With proper timing and process, the durability of the concrete is not affected.
Typical scaling of concrete slab due to rain on nondurable paste surface
Worst case: The concrete is not protected from the rain; the water is not allowed to evaporate from the slab surface; and multiple passes of the floats and trowels used to finish the surface are made with the surface moisture in place. The energy supplied by the finishing operations mixes the excess water into the slab surface creating a high w/c ratio in the near surface of the concrete reducing its strength and thus its durability. In the worst situation, the damage to the concrete surface is readily apparent since the texture of the surface is easily damaged or removed after the initial curing period. (If the surface is dusty after 14 days of curing there a likely to be a problem.) If the surface strength is only slightly affected, the long term durability of the concrete may be reduced as evidenced by a general loss of the surface mortar (scaling) after the concrete has been through a winter season of freezing and thawing cycles; however, the concrete strength and durability below the surface would not be affected.
In most cases concrete is warranted for one year, which will allow you to assess the potential durability of the concrete surface, and in instances similar to this one many contractors are willing to extend the warranty for an additional period of time (an extra year or two) to settle the doubt.
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Note that I did see them cover the freshly poured concrete a few times, most specially on January when it was raining non-stop in Vcr for 28 days. But other than that, including today, there is no covering...