One option is to lay concrete block up off the interior ledge of the footers to just below where the concrete slab will be. You can also fill the trenches with a gravel product that's a mixture of washed sand and different sizes of rounded gravel. The center of the garage area is undisturbed dirt and rock that's been there since the dinosaurs roamed. At this stage of the project, with not even a floor to stand on or a roof to hide under, cars and trees were the only shelter available. The total length of the tamper should be 22.5 cms more than the width of the slab. The terminology used for soil support systems, unfortunately, is not completely consistent, so let's follow the American Concrete Institute's definitions, starting from the bottom: 1. For a slab on ground construction such as 60k House, the concrete slab needs to sit on a solid, level base. Fernando Ferrari, s/n, Goiabeiras, Vitória, ES, CEP 29060-900, Brazil calmont@npd.ufes.br My builder says he's just going to fill it in with the dirt he dug out and all will be well. I see photos of this unnecessary damage all the time. Sign up to my newsletter to receive expert advice for your home! It is important to prepare the slab bedding correctly. It is applied at sites where vibration is very difficult or even impossible (such as underwater). If you have to use crushed stone, be aware that it requires mechanical compaction so the pieces of gravel interlock. The result is almost always a crack and the concrete slab drops down. © 2017 Tim Carter. It can also ensure the correct level of the surface. You lay block up off the footing so it comes to the bottom of the slab. 11.2. We're going to have probably 12 of fill, If the lift being tested fails to meet density specifications, that lift should be reworked until it meets the desired specifications. A concrete driveway should last for decades if it’s properly installed. This gravel is the size of small green peas and it naturally compacts as it's put into a void space. Make sure all debris, stones and plant material are removed before levelling and compacting the soil to create a level base. It doesn’t matter how big or small your concrete pour is, the first step is to prepare the ground. Subscribe to the FREE Ask the Builder newsletter to receive professional advice for your home. It had rained over night so we also bailed out the water that had become trapped by the blockwork and collected at the low point. Step 2. You're correct that the dirt in the center of the garage area is solid fill. A layer of gravel was then scooped in to provide the bulk of the fill. Because the site is on a slope we needed to raise the level of the base within the perimeter blockwork with fill. Using something else for fill (sand, aggregate, etc.) Dirty, loud, shaky work: Luke on the ‘whacker packer’ compacting the gravel fill, The ‘whacker packer’ sits silent as the sand waits to be spread across the FCR. www.MattRisinger.comThe most common foundation in the South is a Slab On Grade. Self- compacting concrete (SCC) is a special type of concrete mix that can be cast without compaction or vibration. On top of the gravel went a 200mm layer of FCR (fine crushed rock/blue metal). SCC is quick to apply, leading to savings in staff costs. How to Level a Site for a Concrete Slab. Concrete mix proportions are designed to achieve it desired properties it’s placing, compaction and curing are also critical to realize potential of a concrete as an end product. The plumbing that will be within or beneath the concrete slab also needs to be installed at this time. You place these piers about 4-feet-on-center around the entire slab. The three ingredients to attain … Each has to be studied to see which is the most cost effective. Backfill beneath concrete flat-work along foundation walls should be accomplished with a granular material that is uniform in size. As each layer of loose fill is compacted, density tests should be done as directed by the geotechnical staff. CURING THE CONCRETE SLAB (PROTECTING THE SURFACE AGAINST MOISTURE LOSS) Moisten the surface and edges of the slab using a hose on a gentle spray twice daily for 7 days. What would you do? Subbase is a layer of gravel, which is fairly cheap material, placed on top … DEAR TIM: My new home is under construction. Compacting Soil For Concrete Slab Foundation compacting sand and clay concrete foundation soil erosion under concrete lift up subgrades subbases for concrete slabs why do concrete slabs sink mixan. If un-compacted, or poorly compacted, soil or fill sinks under a slab you end up with a hollow spot. Your email address will not be published. It can jump around if it hits a hard spot. Good finishing techniques will make a slab look great for a while, but proper ground prep will keep your concrete crack-free for years. Mixing, transporting, and handling of concrete should be cautiously synchronized with placing and finishing operations. Many builders don't take this extra time. Although honestly, I don't see this arrangement as much different than my house foundation except the open space/soil is reversed. Details provided are in good faith and relate specifically to this project. When fill dirt is placed in large amounts for highways and other projects, the fluffed dirt is brought in, spread out in thin layers and then compacted by large machinery designed to compact dirt and rock. CLICK HERE to Get Tim's FREE & FUNNY Newsletter. When compacting soils more is always better but it takes time and that costs money. Your builder can use the soil he dug out of the ground to fill the trenches back in, but to do it right requires lots of work. First piece of floor insulation in place, Costs: gravel – $448; FCR – $544; earthworks – $500; plumber – $399. The plumbing work is done by a licensed plumber and the location checked by a council plumbing inspector. The dirt and rock in the center of the future garage has been compacted by Mother Nature for eons. I preferred to use washed pea gravel for filling trenches like this in garages. Compacting the foundation and floor with a compactor (whacker). The recycled concrete does compact well using rollers or plate compactors, but as you said, that’s very tough to do in your case. However at the end of the day and with the first piece of floor insulation in place Greg the builder still managed a smile , Is that a smile? If you drive on this concrete and apply pressure to it, the concrete tries to bend or stretch to conform to the hollow spot. If you pour your concrete on uneven ground, the slab may look crooked or get damaged as it dries. Right now there's a trench around the inside on all four walls where they had to dig to install the foundation. For compacting a concrete slab such as for roads, floors etc. Re: compacting gravel under a slab Thanks for your comment Dick, but hopefully they'll be no "oozing" of concrete into the gravel under this slab. Your builder has all sorts of options if he doesn't want to go to all that work. The result is almost always a crack and the concrete slab drops down. Preparing to fill: bailing out the water, removing the topsoil and knocking out the knock-out blocks. The slab then acts as a bridge between the pilasters and the compact dirt in the center of the garage. You may be lucky to have a gravel company that has a truck equipped with a conveyor belt that will shoot the gravel in place so very little work has to be done by hand. Concrete has tremendous compressive strength. If you drive on this concrete and apply pressure to it, the concrete tries to bend or stretch to conform to the hollow spot. I'm in a disagreement with my builder about what's going to happen under my garage slab. Not compacting the fill will allow my slab to settle. Filling & Compacting Products If you are looking for some filling material to fill a hole, stabilize some boggy ground or prepare an area for a concrete slab or pavers, Centenary Landscaping Supplies has a complete range to choose from. Filling and Compacting Getting down and dirty. This applies to the overdig area as well as the raised sub-base underneath the slab. If uncompacted, or poorly compacted, soil or fill sinks under a slab you end up with a hollow spot. The moisture content of the fill dirt is important as is every other facet of the operation. Concrete slabs may be constructed on filled sites only where the placement of the fill has been strictly controlled. Generally if you are spreading 4-12 inches ¾ inch clean crushed stone on undisturbed soil that is about as good as you are likely to get for residential construction. How to Compact Soil for Concrete Slab Step 1. This extra step is costly and it must be done correctly so your slab never fails. The end of a long, wet day. Tom M., Binghampton, NY. But the exact same concrete mix, when you stretch or bend it, engineers call this tension, has on average only one tenth the strength as it has in compression. To compact the materials we used what is affectionately known as a ‘whacker packer’ (compactor). Because of the area of the concrete slab a strip thickening is needed to strengthen the slab – an additional footing to the one around the outer edge. SELF-COMPACTING CONCRETE USING MARBLE AND GRANITE SAWING WASTES AS FILLER João Luiz CALMON1 Mirko MORATTI1 Sandra MORAES1 Daniela CENCI1 1Graduate Program in Civil Engineering, Technological Center, Espirito Santo Federal University, Av. Building a store room. I was lucky to build in an area where there was abundant rounded sand and gravel. Concrete floor problems building science corporation how to lay a gravel shed foundation an everyday homeowners guide proper subgrade prep concrete construction magazine building a greenhouse foundation view of a the concrete slab over vault edge beams and b subgrades subbases for concrete slabs the network. This means if you squeeze it, it often takes 3,000, 4,000 or more pounds of pressure per square inch to get it to crack and fail. Concrete is an amazing material, but it has an Achilles heel. Fill the void spaces with self-compacting gravel like the green pea gravel you see. Page 3 of 7 > compaction of concrete Table 1 Characteristics and applications of immersion vibrators Diameter Recommended Average Radius of Rate of concrete of head 2frequency1 3,5amplitude action placement 4,5 (mm) (Hz) (mm) (mm) (m3/h per vibrator) Application 20–40 150–250 0.4–0.8 75–150 1–4 High slump concrete in very thin Each time a vehicle pulls into a garage and stops, that action creates a plate compactor effect. But the trenches next to the new foundation require special care by the builder. Concrete slabs have a variety of uses, including home foundations, walkways, and patios. Step 3. Prepare slab bedding. counter this, one answer is to place concrete up to the underside of the ducts, wait half an hour, re-vibrate and then continue placing and compacting. Disclaimer: Any advice contained within this blog is of a general nature only and cannot be relied upon. The slab could be for an entire home, it might be an exterior patio slab, a front porch slab, a driveway, etc. A soil engineer can develop a compaction plan that speaks to the amount of soil that can go in the trench at a time, the fancy name for this is a lift, what tool needs to be used to compact the soil and how long the tool needs to be used to get the soil compact. The plumbing that will be within or beneath the concrete slab also needs to be installed at this time. When packed tightly, however, the gravel doesn't shift beneath the concrete. “Self compacting” turns out to be about 80% true. Solid Pave can handle all aspects of your concrete construction including, proper foundation measurement, installing fill dirt, grading and compacting the slab area, wire mesh reinforcement, termite treatment, vapor barrier installation, and forming and pouring the concrete slab. is going to cost a fortune. When all that ice melted on it's own with no help from us, it created untold cubic yards of this wonderful rounded gravel. This is 1/2-inch rebar. Compaction also helps to get the concrete to surround all the reinforcement steel and to fill all corners of the form, however small they may be. The easiest fix to the situation in my opinion is to just fill the trenches with self-compacting gravel. This involves excavating to the required depth: for strip footings this is generally to undisturbed ground, while for pad foundations and floor slabs you will need to allow enough depth for your sub base and damp-proof membrane (dpm) as well as the concrete. Adding water to fluffed or disturbed soil will go a long way to accelerate natural compaction of soil particles. If he does use the dirt is there a special way to install it? Spray down the slab area with water. DEAR TOM: Un-compacted fill under concrete slabs of any type is a recipe for disaster. These can be spaced at 4-foot intervals around the interior foundation walls. Static compaction is confined to upper soil layers and is limited to any appreciable depth. This is referred to as 'controlled fill'. The excavator was used to remove the layer of top soil and clay. “I recommend open-graded granular material be used,” says Tull. Required fields are marked *. Soil Settles. I'll have a layer of thick poly ontop of the gravel then a layer of 2 inch rigid insulation under the slab. Compaction should be applied uniformly to the entire concrete mass. Are there other things that can be done? Mother Nature, over time, does an amazing job of compacting soils. Forming the concrete strip thickening in the middle of the slab. Here's a quick drawing I made showing the concrete block ledges. a steel shod wooden tamping beam or screed is used as shown in Fig. This means the fill material has been carefully selected and compacted in accordance with the procedure set out in AS 2870. Use a steel-tined rake to rake the soil level. Hand and pocket knife for scale. This was created by the massive continental glaciers that covered much of the northeast USA and the upper Midwest about 15,000 years ago. Complete the form below and each week you'll get: Unsubscribe at any time. For 60k House only the plumbing for the bathroom will be below the floor; the plumbing for the kitchen will be within the wall cavity and can be done later once the walls are framed up. Another task was to knock off the backs and sides of the knock-out blocks with a sledgehammer. What should be done? The slab will have to have steel rebar, no less than one-half-inch in diameter in both directions spaced at 2-foot centers to make this work. Here are some great tips on how to prepare the site for a pour. The only way to change the effective compaction force is by adding or subtracting the weight of the machine. Subgrade—this is the Static forceis simply the deadweight of the machine, applying downward force on the soil surface, compressing the soil particles. Typically, coarse clean sandy soils are used for this purpose. Finally a 50mm layer of sand was spread evenly on top. The rods are almost always 20-feet long. Each layer needs to be compacted before adding another layer on top (this minimises any settling or subsidence that cause the concrete slab to move or crack). Visit a few local gravel pits in your area to see if they have this small rounded gravel. This is a side view showing just one of the supports. Some fill materials, such as round stones like pea gravel, tend to be self compacting. CLICK HERE to get FREE & FAST BIDS from local concrete slab contractors. Your email address will not be published. Any author will not be held responsible for advice or information presented. Prep for Crack-Free Concrete. Curing must start the same day – as soon as you have finished the surface. “When using a plate compactor on fill,” says Mike Murray with Concrete Cares, “we recommend placing 3-inch lifts—the plate compactor doesn’t provide enough force for a 6-inch lift.” The maximum compaction of any granular material can only be achieved at the optimum moisture content. We respect your email privacy. If concrete is well compacted, we achieve durable concrete, but over compaction also leads to the segregation of concrete. The thickening will reduce the likelihood of movement in the slab that might cause it to crack. The same process can be done for smaller jobs like yours. This will ensure that the … The concrete slab will rest on these and provide solid support down to the footer. Rainwater plays an important part of this process. Uncompacted fill under a concrete slab — be it for an entire home, an exterior patio, a front porch or a driveway — is a recipe for disaster. Notice that each layer of material is much finer than the previous one. Craig the plumber installing the pipe for the floor waste to the shower/bath, This was the first wet day we had while working on site. Curing provides a continuous supply of moisture to ensure a better surface quality and a stronger slab. This product requires water to get it to naturally compact and you need to install it in layers no thicker than one foot at a time. If un-compacted, or poorly compacted, soil or fill sinks under a slab you end up with a hollow spot. Remove any rocks that may be in the soil. Plumbing. Subbase for Concrete Slab. Maybe the difference is I'm not compacting the back fill against my foundation. The thickening is not exactly in the centre but will sit below a masonry wall made from recycled bricks – heavier than a standard timber framed wall. Re-vibration is fine as long as concrete is still workable enough.To assess this, insert a poker and if it sinks into the concrete and leaves no hole when removed, the concrete can be re-vibrated. When I was still building on a daily basis, I would go to great lengths to water the fill soil in utility trenches and around the outside of a new home to get the soil to settle faster. Must be careful for your feet. © 2017 Tim Carter. I think that's a mistake. © 2017 Tim Carter. This is what I used to do on my jobs. The steel bars need to be placed so they line up with the concrete block pilasters. Bricks, Masonry, Cinder Block, Paving & Walking Stones, Asphalt and Concrete - Compacting sand - What's the proper way to compact sand beneath a new slab? If the backfill under the slab has not been properly compacted, the structural fill will eventually settle, leaving voids.