Avoiding Raveling of Pervious Concrete

sometimes rocks can come loose from pervious concrete this is known as raveling though unsightly raveling is a superficial problem not affecting the entire depth of the pavement only the topmost layer it's usually most prevalent along the edges and joints if raveling does occur it begins to show up within a few weeks of placements and then winds down being mostly done after about 4 months it can be common with pervious concrete but extreme raveling can always be avoided if you understand why it happens evaporation is the main reason there are many factors that contribute to evaporation and make pervious concrete particularly vulnerable to the effects of it pervious concrete has voids and allow water to pass through it these voids give the material a large surface area this means the topmost layer of the freshly placed pavement has a lot of contact with the air the more contact with the air the more evaporation occurs for this reason pervious concrete differs significantly from ordinary concrete's and has its own unique timing and placing considerations with ordinary concrete excess water known as bleed water slowly rises to the top after placement replacing the water on the surface that is lost to evaporation pervious concrete on the other hand it doesn't have any excess water to give the window to get just the right amount of water in the mix is extremely narrow pervious concrete basically consists of a thin layer of cement paste coating each piece of aggregate since the cement paste is so thin water that evaporates does not get replaced if this cement coating dries past a certain point before it has a chance to set the bond between the aggregate particles will be compromised shortly after placing the bond can fail and rock will come loose in this way too much evaporation can lead to raveling the rate of evaporation is affected by the surface area wind humidity and most of all temperature pavement in full Sun can have a surface temperature well above ambient this can lead to an alarming rate of evaporation even on a fairly cool day surfaces can reach temperatures well into the hundreds above 50 cell this can be disastrous for a pervious concrete installation it doesn't take much to exceed the critical point if just 5% of the mix water has evaporated from the surface of the pervious concrete it will become noticeably stiffer and may begin to tear as you're working it at this point the pervious concrete surface begins to become unworkable or unfinish Abul it becomes harder to blend and apply the final finish an unworkable consistency is a sign that too much evaporation has occurred if you work past this point and apply the final finish anyway there will likely be raveling of the surface later on pervious concrete made with small aggregates not only has a larger surface area but it also has a thinner coating of cement paste around each grain the thinner the paste the more susceptible it is to the effects of evaporation a 3/8 aggregates can become unfinishable within 5 minutes when left in full, midday sun but a small aggregate less than eighth of an inch can become unfinishable in as little as two minutes of sun exposure but despite the shorter working time we still prefer fine aggregate pervious concrete for aesthetic reasons. not only is the surface smoother but if raveling does occur it's less noticeable. to combat raveling you must plan to put environmental conditions to your advantage having the pervious concrete in full shade rather than full Sun can easily lengthen the working time by a factor of five or more there are evaporation reducing and offsetting add mixtures for pervious concrete but so far none come close to having this level of impact on working time attention to the following four points will provide the greatest insurance against traveling make sure your pervious concrete is optimally hydrated and kept cool check out our video how to make pervious concrete for more info on this carefully consider the weather during your installation install the concrete quickly and steadily compacting in a timely manner and make sure the concrete is properly cured keep your pervious concrete cool before and during mixing and we'll have a longer working time if your mix is hot a lot of water will evaporate before you even get a chance to play on the ground if your concrete has to travel far between the mixing site and the installation you may want to add additional water to account for this if you're mixing on-site keep your mixer in the shade if you need to leave the mixer going for a long time periodically add more water to prevent the mix from drying out too much if getting your pervious concrete from a batch or Ready Mix plants don't expect the delivery of a perfect mix you need to know what to look for with every load and be able to adjust accordingly the start early to take full advantage of the morning weather and have everything prepared a day or two in advance this includes having the base properly compacted and soaked with water joints marked and all your tools and materials on hand if you anticipate needing to pour in less than ideal conditions or you have a small crew you can extend the working time of your pervious concrete by setting up shade canopies or shade fabric to keep the pervious concrete out of the hot Sun misting fans can be used to humidify the installation area just be careful if water from the misters condenses on overhanging shrubs or a shade canopy and drips onto the concrete it can wash away paste and cause raffling this can also happen if the pervious concrete gets rained on before it is covered in plastic if this happens you may have time to cover the spot with fresh material and refinish it but if the concrete has already begun to set it's best to leave it be we like to use high pressure missing systems so the water droplets are very small we found that non-pressurized misters put out drops of water that are too big large droplets of water can fall and wash away the paste use spray bottles to mist specific areas that are drying out as the morning gets a little warmer and drier we spray the pervious concrete on the ground before blending it with the next batch if a section of pervious concrete has dried out before getting a chance to finish it mist it to replenish some of the water and blend in fresh material to make it more workable the faster the pervious concrete is placed and finished the better the material is easier to work with when it's fresh so you can work faster if you work faster you will always be working while the pervy as concrete is fresh so it will take less time to apply the final finish for this reason the pour becomes almost exponentially faster if there are more workers provided they can all work in the confines of the space placing pervious concrete continuously finishing as you go will help ensure a strong surface free of raveling if the crew is bigger experienced enough it can be best to pour the entire width of the pavement at once as we did for this driveway extra wide areas are more manageable if poured in separate sections divided by a joint which can be created by placing a temporary form between them when coming back to fill in sections be very careful not to disturb the edge of the existing pervious concrete pervious concrete that is disturbed after it has begun to set is very likely to Ravel raveling appears most commonly along edges and joints so these areas require extra attention we prefer to make joints by using wedges that will compact the pervious concrete not cut it when it first goes down step on the pervious concrete along the edges and forms as these areas are difficult to compact later on then add more material over what you compacted and finish with an edger leaving a compacted rounded edge place joints and edges as soon as possible waiting too long to install a joint can dislodge aggregate that was already set in place leading to raveling timing is key with all concrete placements pervious concrete with its own unique timing can be summarized as place as fast as possible with pervious concrete there really isn't a way to place it too fast perhaps the only caveat being if the mix is too wet to begin with finishing early can make it sealed up with our very fine mixes sealing up is rarely a problem and in general we find it much easier to get a more consistent texture we like to finish our fine mixes first by using a magnesium or aluminum floats to level and blend areas and then follow with a steel trowel however we don't typically recommend steel trowel for pervious concrete made with coarser aggregates because of their thicker paste they can easily seal up when finished with a steel trowel or Fresno sealing up can be minimized by using a wood a resin float for the initial smoothing and blending and then a magnesium or aluminum float for the final finishing if a section appears sealed up dig it out right away and fill with fresh material on large installations of pervious concrete rotating pizza pan type finishers seem to be able to provide just the right touch that can minimize the occurrence of sealed up areas and provide a nice overall finish the degree and timing of the compaction of the fresh pervious concrete can make a big impact on raffling in general the sooner the compaction is applied the less force is needed for very fine aggregates we find the compaction provided by the steel trowel is adequate however steel Fresno's with twenty pounds or so of weights can also be used coarser mixes require more compaction than can be done by hand in large applications spin screeds are often used followed by a heavy cross roller if the cross roller is used it could be better to run it over the plastic to minimize the amount of aggregate that sticks to it when doing this however you should periodically check under the plastic to ensure the pavement isn't being overly compacted and sealed up in some situations and magnesium both float with at least 20 pounds of weight may be adequate for other applications equipment like this trail rider can place and compact pervious concrete at the same time making for even faster installations we've been discussing reducing evaporation and causes of raveling during the installation process but equally important is the curing process the water in the concrete that we've been working so hard to maintain must now he locked in to ensure the pervious concrete can properly hydrate and cure over the following days to do this immediately cover each section with plastic as it is completed create a tight seal by overlapping all the edges and use plenty of boards and other heavy objects to weigh the plastic down so it doesn't blow away later wait at least four days before removing the ply many recommends seven days or more most instances of raveling in pervious concrete can be avoided by paying attention to evaporation however there are a couple other potential causes worth addressing as well we mentioned earlier that overhead water can lead to raveling but a similar thing can happen if the mix is just too wet to begin with the paste can drain off the surface of the aggregate if this should occur it's best to mix the overly wet material with fresh drier material then Rees pred pervious concrete can be a great solution in colder climates however if de-icing salts are used before the pavement has properly cured or if it wasn't designed to withstand them this could also lead to raveling if you happen to cross this video too late and there is raveling in your pervious concrete we have outlined several solutions on our website pervious products calm

Channel: Pervious Products

Views: 31,578

Keywords: Pervious Concrete, raveling, thristy concrete, permeable concrete

Id: xkkgTXbYvBI

Length: 12min 7sec (727 seconds)

Published: Fri Oct 19 2018