Grout Mixing and Pumping
March 1, 2012
Because a wide variety of materials are available for many different applications, it is incumbent upon the operator to become familiar with the specific characteristics of the material to be used to ensure a successful application. ChemGrout Inc. offers these salient tips to ensure optimum performance.
Get in the FlowIn general, most materials need to be of a flowable or pourable consistency for successful pumping. This means that if the material can be poured out of a pail or bucket, it likely can be pumped. The exception to this requirement is repair mortars, which tend to be mixed in a thicker consistency, and require special pumping techniques. Materials that contain aggregates pump best and perform best when the consistency is kept to the lower range of pourable – that is, not too wet.
Setting TimeSome materials contain accelerating admixtures to reduce the setting time. This particularly is true of repair mortars and other spray-applied materials, so that strength gain can be fairly rapid. It is important to keep moving when using these types of materials. Once the material is mixed, it must be pumped immediately and kept in motion, and subsequent batches must be mixed and pumped as rapidly as possible. Any delays in the application process could result in plugged hoses and equipment. Temperature also has an effect upon these materials to the extent that exposure of the hose to the sun on a hot day will accelerate the set time even more; therefore, this should be avoided. It even may be necessary, in some cases, to cool the material, the mix water or even the hose itself.
Pumping DistancePumping distances always should be kept to a minimum, and hoses should run as straight as possible – no matter what material is being used. Sometimes, circumstances require longer-than-usual hose lengths; when this occurs, every effort should be made to use every advantage possible to ensure a successful application. Some materials simply cannot be pumped for long distances, so it’s best to know the proposed material characteristics before attempting a production procedure.
General ProceduresBefore attempting to mix and pump production materials, it is prudent to rinse the mixer and charge the pump hopper with sufficient water to thoroughly flush the pump and all grout lines. This is to purge the grouting system of any residual materials or scale that may exist. Once that is completed, remove the grout hose from the pump, and drain out all water by elevating one end, or by progressively elevating the entire hose, starting at one end and proceeding to the other.
Next, mix a slurry, composed of portland cement in approximate proportions of 61⁄2 gallons to 71⁄2 gallons of water to one bag (94 lbs.) of cement, and pump this through the grouting system. This is to remove any residual water from the hose, lubricating it for the production material to follow. Now the production grout may be mixed and pumped immediately behind the slurry mix, which is thus evacuated from the hose, and may be retrieved in a bucket. Do not attempt to pump production material through a dry hose.
One last word about procedures: Occasionally, no matter how conscientious an operator may be, a hose will get plugged. Once this happens, the only sure way to remove the plug is to empty it of material. Beating on it with a hammer or running over it with a vehicle usually will not be successful. A prudent operator will be prepared for such eventuality by having readily available a sufficient length of small-diameter stiff tubing, hose or plastic pipe to which he can rapidly connect a water source, and flush the grout from the hose.
Grout Pumping TipsIn general, the most important factors in setting up are proximity to the work and access to materials and water supply. Consideration also should be given to the disposal of waste materials and wash-out residue.
It is always best to keep grout lines as short as possible to reduce pumping distances. This is particularly important when pumping hard-to-pump materials, such as sanded grouts and pre-blended materials.
The source of solid materials (cement, fly ash, sand, etc.) should be readily accessible and an adequate supply of water should be available for mixing and clean-up. When planning a project for high production rates, remember that the greatest consumption of time occurs when charging the mixers. A proper set-up can reduce this to a minimum.
Start-up PhaseAfter setup, visually inspect that there are no foreign objects or old setup materials in either the pump or the mixer(s), then make all necessary connections. With operating levers, valves or handles in either neutral or off position, and the primary power source turned off, fill the pump hopper with clear water. Turn on the primary power source, and observe that conditions are normal and the machine is ready to run.
Check each mixer for proper operation by running the mixer in both forward and reverse directions (if unit is so constructed as to allow reverse direction). Next, start the delivery pump to discharge the water that was previously introduced into the pump hopper. This is an ideal opportunity to check the grouting system to determine that all lines and hoses are clear and unobstructed. Pump condition also may be checked at this time by testing the discharge pressure. When it is determined that all systems are normal, shut off the pump, and drain the water from the pump and all lines.
Some pre-blended materials and some on-site mixes of sand and cement tend to separate and clog the hoses upon contact with residual water in the hose; so it’s a good procedure to mix and pump out a cement/water slurry prior to mixing and pumping the production material in order to lubricate the pump and hoses.
Production PhaseDuring the production phase of the work, continuously monitor pump and mixer performance, being alert to any signs of abnormality. Keep mixers free of material build-up; keep the outside of the machine clean; and keep the pump packing lubricated and just tight enough to prevent leakage.
Clean-up IssuesAfter disposing of excess production material, carefully wash out mixer tanks, paddles and baffles into the pump hopper, and pump the resulting washout material through the grout hoses to a suitable disposal site. Continue this operation until only clear water is discharged. It is advisable to drain all residual wash water from the pump and all hoses when washout is complete.
- Never run the pump without fluid, as it will cause severe
damage to the pump.
- Use safety straps on all grout hose connections.
- Keep arms, hands, fingers, etc., away from moving
- Lock out controls before attempting to clean or repair equipment.
Mixing ProceduresLoad approximately 80 percent of the water anticipated for the size batch to be mixed, and with the mixer running, slowly add the required amount of cement. Allow sufficient time for the slurry to mix to a creamy consistency before pumping or adding filler materials (sand, fly ash, etc.) Slowly add sand (if required) until the mix just begins to lose the cement color. This should be the maximum amount of sand the mix can accommodate, and it may be necessary to use slightly less sand for subsequent batches. The water may be adjusted for the relative wetness or dryness of the sand to produce a grout that is just pourable.
Premix GroutsMany building material suppliers manufacture pre-blended portland cement-based grouts, which may or not be pumpable. Before attempting to pump a pre-blended grout material, determine whether the material conforms to the criteria described above. It also is necessary to determine whether the material has a short working time before set, because there may be insufficient working time to pump. Before pumping any pre-blended cement-based grout mix, it is good practice to first coat the pump and lines with a cement-and-water slurry mix prior to pumping the grout mix.
Homemade GroutsSometimes, commercially prepared grouts are not readily available, and, in these cases, it may be necessary to formulate and produce the material on site. This can be done quite successfully, but certain basic principles must be observed. The resultant material should be a stable suspension of solids that does not separate while at rest. Its color must be predominantly that of the cement used. It also should be fluid enough to pour from a container, but not too wet (thick batter consistency).
Portland CementsThere are several types of portland cements manufactured to satisfy a variety of specific requirements, such as high early strength, sulfate-resistance and other needs. The most common of these is type I Portland cement, which is most frequently used in the production of cementitious grout.
Water ConcernsIn most instances, the water to be used for the production of grout should be clean and free of sulfates or other dissolved chemicals. If available, potable water is ideal. Since the water-to-cement ratio is the most important factor in the quality of the material in its final state, the water content should be kept to the minimum that will produce materials with the proper characteristics.
Those AdmixturesAdmixtures are available to modify and enhance the grout mixture. These include plasticizers, water-reducing agents, expansive agents, anti-washout ingredients and others. If used at all, they should be used only with a full understanding of their effects, and only according to the manufacturer’s recommendations.
Flyash's RoleIn some parts of the country, flyash (a byproduct of coal-burning power stations) is available. This material often has been used to enhance the properties of cementitious grouts, or to reduce the cement fraction in some cases. Use of this material should be approached with caution, since ashes from some sources have been observed to cause flash set in grout mixes. If the use of this product is anticipated, trial mixes should be made to prove its applicability.
Sand ConsiderationsIf the use of sand is anticipated, several factors must be considered, such as the shape, size and gradation of the sand to be used. In general, the sand should be clean, well-graded, and of rounded, natural shape. Angular particles such as manufactured sands should be avoided. Larger amounts of well-graded and round-shaped sand particles may be used in the mix than sand, which is poorly graded or has a significant number of flat, sharp or angular particles. Concrete sand usually is not pumpable, but masonry and plaster sands usually are.