702 - Mortar and Grout
Mortar and/or grout are a mixture of cement, fine aggregate, admixtures (if required) and water. Though mortar and grout are comprised of the same materials, a mortar is stiff and holds its shape, while a grout is fluid and is able to flow into small voids and may be pumped into final position via pressure. Mortars are used to fix small concrete spalls, or in brick or block construction. Grout is used to flow into small voids, anchor dowels and/or provide cover for post tensioning rods and tendons. Grout can be pumped through grout pumps and typically used for post tensioning operations and establishing bearing above and below bridge bearings, beam top flanges, or in other difficult to reach areas.
Non-shrink grouts are typically prepackaged mixes that will maintain original volume as the grout cures. These are best suited for most grouting operations to eliminate the risk of concrete shrinkage and creating a lack of bearing or cover.
Expansive grouts are mixed according to specifications and contain an expansive admixture that creates a 5-10% increase in volume. They also contain very little chlorides and thus are ideal for protecting high stressed steel tendons.
Mortars and grouts may be remixed, however; they may not be retempered. Mortars and grouts may NOT be reused once they begin to set.
Mortars and grouts must only be placed when temperatures are at least 40 degrees Fahrenheit during the placement and curing period.
When practical, a wet cure should be utilized for at least 7 days to prevent drying, shrinkage and cracking of the grout.
Materials must be selected in accordance with subsection 702.02 of the Standard Specifications for Construction.
|Portland Cement Type I, Type IA||901|
|Masonry Cement Type N, Type S, Type M||901|
|Hydrated Lime Type S, Type SA||901|
|Air - Entraining Admixture||901|
|Fine Aggregate 2NS, 2MS||902|
|Specialized Materials For...||See Subsection|
|Non-shrinking Mortars and Grouts||702.03.B|
The cement and fine aggregates must be proportioned by weight for batches of 1 cubic yard or more, and may be proportioned by weight or volume for smaller batches. Tables 702.01A and 702.01B of the Standard Specifications for Construction give the mix proportioning information for standard mortars (R-2 & R-3) and grout (R-1). Water is added in amounts necessary to obtain the consistency required for the work.
Non-shrink mortar and grout must not be used in contact with prestressing tendons or other highly stressed steel, however; may be used for recessed stress pockets on the fascia of beams being post-tensioned.
Non-shrink grout may also be used for dowels and anchor bolts and under level plates and bearings. The non-shrink grouts are a premixed material listed in section 702.02B of Qualified Products List (QPL) found in the MDOT Materials Source Guide. Water is added to the premixed, approved product as directed by the manufacturer to achieve the desired consistency while maintaining the minimum required compressive strength.
Expansive grout, Type E-1, is used for filling the void around post-tensioned tendons in precast concrete box beams. The grout must be proportioned as specified in subsection 702.02.C of the Standard Specifications for Construction.
- No sand is to be used in the grout mixture.
- The grout will attain a 28-day minimum compressive strength of 3000 psi, according to ASTM C 942, however; the grout must be proportioned by MDOT specifications.
- The expansive admixture, including any plasticizing or water reducing agent, must not contain chloride ions >0.50 percent by admixture weight nor any fluorides, sulfides, nitrates or thixotropic additives, or chemicals that may contribute to stress corrosion in steel.
- The admixture may be in liquid or solid form.