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Self-Consolidating Grout for Concrete Masonry

  • August 2018

INTRODUCTION

Self-consolidating grout (SCG) is a specially-formulated grout for use with reinforced masonry. It is designed to fill the long, narrow and sometimes highly congested cores of reinforced walls without the need for consolidation and reconsolidation by mechanical vibration or by puddling.

Self-consolidating grout has been used in various parts of the United States, under the grout demonstration panel provisions of Specification for Masonry Structures (refs. 1, 2), which is included by reference in the International Building Code (refs. 3, 4). The 2008 edition of Specification for Masonry Structures (ref. 5), however, includes explicit provisions for SCG.

Unlike conventional grout and conventional concrete, self consolidating grout (SCG) is a special application of self consolidating concrete (SCC) that uses aggregates complying with ASTM C 404, Standard Specification for Aggregates for Masonry Grout (ref. 6), as specified in ASTM C 476, Standard Specification for Grout for Masonry (ref. 7).

Similar to conventional grout, there are two types of selfconsolidating grout, coarse and fine, with the latter containing only fine aggregate. Coarse self-consolidating grout has been the most common, although fine SCG is predominant in several specific regions of the U.S.

MATERIALS FOR SELF-CONSOLIDATING GROUT

Self-consolidating grout attains a high flow not from adding more water, but from a careful mix design to create a flowable yet highly cohesive grout that will not segregate and can pass freely through congested reinforcement and narrow openings without “blocking or bridging.” SCG must maintain its fluidity without segregation and maintain consistent properties throughout the grout lift. It is composed of aggregates, cementitious materials, water and special admixtures which provide the fluidity and stability to meet performance requirements.

Aggregate Size and Proportion

To obtain the desired filling and placing ability, aggregates used in SCG should meet the requirements of ASTM C 404, as specified in ASTM C 476. The requirements for coarse aggregate, for use in coarse SCG, are essentially the same as the requirements for No. 8 and No. 89 coarse aggregate in ASTM C 33, Standard Specification for Concrete Aggregates (ref. 8): they should be either a Size No. 8 or Size No. 89 gravel, stone or air-cooled iron blast furnace slag with 100% passing the ½ in. (13 mm) sieve and at least 85 to 90% passing the 3/8 in. (9.5 mm) sieve. Fine aggregate, for use in either coarse or fine SCG, is typically Size No. 1, which is a concrete sand as defined in ASTM C 33, but could also be Size No. 2, which is a sand for masonry mortar as defined in ASTM C 144, Specification for Aggregate for Masonry Mortar (ref. 9).

ASTM C 476 contains a proportion specification as well as a performance specification for masonry grout. The proportion specification specifies that coarse grout should have fine aggregate in the amount of 2 1/4 to 3 times the sum of the volume of the cementitious materials and coarse aggregate in the amount of 1 to 2 times the sum of the volume of the cementitious materials. These ASTM C 476 requirements are equivalent to s/a (sand/total aggregate) ratios of approximately 0.50 to 0.60 on an absolute volume basis. By comparison, most self-consolidating concrete mix designs have similar s/a ratios in the 0.50 to 0.60 range.

Cementitious Materials and Minus 100 (0.150 mm) Sieve Content and Composition

Grout is required to have a minimum compressive strength of 2,000 psi (14 MPa) after 28 days of curing (ref. 7). Building Code Requirements for Masonry Structures (ref. 10) sets an upper limit on the specified compressive strength of grout at 5,000 psi (34.5 MPa) at 28 days when using strength design of concrete masonry, although experience indicates that many conventional grouts develop strengths greater than this specification limit. Note that actual strengths are somewhat higher than the specified strength to assure compliance.

In the historical context of masonry materials, the term cementitious materials has commonly referred to the cement content (as well as lime in the case of masonry mortars) used in the manufacturing of masonry units, mortar or grout. In the production of SCG, however, the fraction of very fine aggregate particles present in the mix can have a significant influence on the plastic (and by association, the hardened) properties of SCG, and therefore needs to be considered in the batching of SCG. As such, the ‘powder’ content of an SCG mix, which includes both conventional cementitious materials as well as the very fine aggregate dust smaller than the 100 (0.150 mm) sieve, is monitored to ensure a stable SCG.

Adequate paste content is critical for making stable SCG mixes because the paste forms the matrix in which the particles are suspended. This paste is composed of cementitious materials (including the powder), water and entrained air, if any. The entire powder content of some mixes may contain auxiliary materials including pozzolanic and hydraulic materials, as well as ground limestone and inert fillers. These additions can improve and maintain cohesion and segregation resistance of the mix while lowering the overall cost and helping to control the ultimate strength of the mix.

Although not widely used in the U.S., ground limestone and inert fillers can be very effective in SCG mixes as a means of keeping compressive strengths to the lower range. They should be considered if they are regionally available. Fly ash can also be an effective addition because its use can help enhance the filling ability and slump flow of the mix while providing increased cohesion and reduced sensitivity to changes in water content.

Research has shown that slump flow values are increased when the fly ash replacement rates are between 20 and 40% of portland cement (ref. 11). If the goal is to control compressive strengths, Class F fly ash can be effective because it typically does not contribute as much to strength gain as Type C fly ash. GGBFS (Ground Granulated Blast Furnace Slag) has successfully been used in SCG mixes to replace some of the cement, but its high ultimate strength gain usually means that the compressive strengths of these mixes are usually similar (or sometimes higher) than straight cement mix designs. Research (ref. 12) has demonstrated that coarse SCG mixes could be made with total cementitious materials contents of 750 lb/yd3 (445 kg/m3), and possibly with 700 lb/yd3 (415 kg/m3). By comparison, a typical conventional coarse grout made to the proportion specifications of ASTM C 476 contains about 550 to 700 lb/yd3 (325 to 415 kg/m3) of cementitious materials.

Some limited testing in the CMHA research (ref. 12) demonstrated that fine SCG could be made with total cementitious materials contents in the range of 800 to 850 lb/yd3 (475 to 505 kg/m3). By comparison, a typical conventional fine grout made to the proportion specifications of ASTM C 476 will contain about 700 to 1,000 lb/yd3 (415 to 590 kg/m3) of cementitious materials.

Water Content

The term ‘natural slump’ describes the slump of the grout mix before the polycarboxylate is added. A common procedure for making self consolidating concrete is to set the initial water target to the amount needed to bring the mix to a ‘natural slump’ of 2 to 4 in. (51 to 102 mm). The polycarboxylate is then added to make the mix fluid enough to obtain the desired slump flow. This would also be an acceptable initial water target for making SCG, although CMHA research (ref. 12) indicated that some of the most successful batches of coarse and fine SCG made with the local materials used in the research had initial water targets that yielded a ‘natural slump’ of 6 to 9 in. (152 to 229 mm) before the polycarboxylate was added.

Admixtures

Admixtures are integral to the production of SCG. The primary admixture used to impart fluidity and stability to the SCG mix is a class of high-range water-reducing admixtures known as polycarboxylates (PC). These long-chain polymers are synthesized to help keep the cement grains dispersed while adding some cohesiveness and stability to the SCG mix.

Another class of admixtures often used to make SCG in conjunction with the PC is the Viscosity-Modifying Admixtures (VMA). VMAs help adjust viscosity and can improve the cohesiveness and stability of the mix while allowing it to flow without segregation. Not all PC and VMA products have the same properties. Some PCs impart substantial amounts of stability and cohesiveness to the mix and are recommended to be used without VMA, while others benefit from the addition of VMA.

In the past (before polycarboxylates), there have been indications that in some situations superplasticizers in grout for masonry structures have not performed well because they exhibited a short pot life, meaning the mix quickly lost fluidity and rapid stiffing would follow. Absorption of mix water into the surrounding masonry also negatively impacted the flow. In high-lift grouting (placing grout into grout columns as high as 24 ft (7.3 m)), enough water could be lost to cause the grout to stiffen and bridge before reaching the bottom of the grout column. With the advent of newer high-range water reducers such as polycarboxylates, however, this problem is no longer evident (ref. 13).

Note that proportioning of SCG is not permitted in the field (ref. 5). However, final adjustment of the mix, in accordance with the SCG manufacturer’s recommendations, utilizing water or the same admixture used in the mix is permitted.

SCG PLACEMENT

Self-consolidating grout is pumped or placed into spaces to be grouted using the same procedures as for conventional grout. Research has shown that with SCG there is no need to first remove mortar fins and protrusions exceeding 1/2 in. (13 mm), as is required for conventionally grouted masonry (refs. 3, 4), since SCG is fluid enough to flow around these small obstructions (ref. 13). However, it is important to note that Specification for Masonry Structures currently requires the removal of mortar fins and protrusions exceeding 1/2 in. (13 mm) for both conventional grout and SCG (ref. 5). Note that because SCG is so fluid, it will flow through gaps wider than about 3/8 in.

(10 mm). To contain the grout, therefore, it is recommended to mortar the masonry unit cross webs of cells containing grout in partially grouted construction.

In bond beams, SCG will be adequately contained using conventional grout-stop materials, such as plastic mesh. When filling intermediate bond beams using high-lift grouting, place the grout-stop material in the bed joints both above and below the bond beam to prevent the SCG from rising above the bond beam location.

Once the SCG is placed, consolidation and reconsolidation is not necessary with either coarse or fine SCG.

Documented successful lifts of 12 ft 8 in. (3.9 m) have been achieved by filling the grout columns of 8-in. (203-mm) concrete masonry walls in a single lift in less than a minute using a concrete pump (ref. 13). Other undocumented placements have placed SCG in a single 24-ft (7.3-m) lift. Twenty-four feet (7.3 mm) is the maximum pour height currently permitted by Building Code Requirements for Masonry Structures and Specification for Masonry Structures (refs. 10, 5). Note also that for SCG, grout lift height can equal the grout pour height.

Blowouts have not been shown to be a problem for conventional masonry units in this research nor in field experience. However, specialty units with reduced or removed webs, such as “H-block” or large pilaster or column units, may require reduced lift heights.

No special curing procedures are required when using SCG. When appropriate, standard hot and cold weather construction provisions should be followed, as for other masonry projects. See All-Weather Concrete Masonry Construction, TEK 03-01C (ref. 14), for more detailed information.

SCG QUALITY ASSURANCE AND QUALITY CONTROL

Specification for Masonry Structures (ref. 5) requires SCG to:

  • meet the material requirements of ASTM C 476,
  • attain the specified compressive strength or 2,000 psi (13.79 MPa), whichever is greater, at 28 days when tested in accordance with ASTM C 1019 (ref. 15),
  • have a slump flow of 24 to 30 in. (610 to 762 mm) as determined by ASTM C 1611 (ref. 16), and
  • have a Visual Stability Index (VSI) less than or equal to 1 as determined in accordance with ASTM C 1611, Appendix X.1.

The ASTM C 476 material requirements are described in Grout for Concrete Masonry, TEK 09-04A (ref. 17). Other quality assurance and quality control provisions related to SCG are described below.

Some methods commonly used for self-consolidating concrete to evaluate passing ability, like the L-Box or J-Ring, are not normally used with SCG because experience indicates that the 3/8 in. (9.5 mm) maximum aggregate size used in SCG has adequate passing ability in masonry grouting applications.

Compressive Strength Testing of SCG Mixes

The current edition of ASTM C 1019, Standard Test Method for Sampling and Testing Grout (ref. 15), addresses the testing of SCG. The procedure for testing SCG is very similar to that for conventional grout, except that SCG is placed in the mold in one lift instead of two and SCG does not need to be rodded.

Slump Flow

The slump flow test method defined in ASTM C 1611/C 1611M, Standard Test Method for Slump Flow of Self-Consolidating Concrete (ref. 16) is used to monitor the consistency of fresh, unhardened SCG and its unconfined flow potential. It is particularly useful to assess the batch-to-batch consistency of SCG supplied over time.

Because of the fluid nature of SCG, traditional measures of consistency, such as the ASTM C 143 (ref. 18) slump test, are not applicable to SCG. The slump flow test is an adaptation of the ASTM C 143 slump cone test. In the slump flow test, SCG is loaded into an inverted slump cone in a single lift without consolidation. The cone is removed and the diameter of the grout slump flow is measured (see Figure 1).

Visual Stability Index (VSI)

VSI, also defined in ASTM C 1611, is performed after the slump flow test to provide a qualitative assessment of the SCG’s stability. The SCG patty resulting from the slump flow test is examined for aggregate segregation, bleeding and evidence of a mortar halo (a cement paste or mortar ring that has clearly separated from the coarse aggregate, around the outside circumference of the SCG patty). The SCG mix is then assigned a VSI, from 0 (highly stable) to 3 (highly unstable).

Although not required by Specification for Masonry Structures, T20 (T50) records the time it takes, during the slump flow test, for the outer edge of the SCG patty to reach a diameter of 20 in. (508 mm) from the time the mold is first raised. It is an optional test for self consolidating concrete, and is similarly applicable to SCG to provide a relative measure of the unconfined flow rate and an indication of the relative viscosity of the SCG. While the actual target value for T20 (T50) can vary for different SCG mixes, it has value in verifying the consistency between SCG batches delivered to the job site.

Self-Healing Ability ‘S’ Test

The ‘S’ test can also be used to help determine the stability of an SCG mix. While this is not a standardized test method, it is adapted from a simple test that is done by some practitioners in the field. There is a common version and a modified version, which gives an indication of the relative segregation resistance of the SCG when subjected to local vibration.

The common self-healing (non-disturbed) test is performed after the slump flow, T20 (T50) and VSI have been recorded. A 10- to 12-in. (254- to 305-mm) ‘S’ is drawn in the SCG patty with a finger, making sure to scrape off the SCG all the way down to the board. The patty is observed to see if the ‘S’ will self-heal. In cases where the self healing is excellent, the SCG flows back together and there is little or no evidence of the ‘S’ remaining. In cases where the self-healing is poor, the SCG does not flow back together and the ‘S’ remains very visible with severe aggregate, paste or water segregation.

Due to observations during the CMHA research (ref. 12), a self healing (after agitate) test was created. After completing the common self-healing test, the SCG patty is vibrated and a second test, designated self-healing (after agitate), is performed. To vibrate the mix, the side of the slump flow baseplate is lightly kicked or tapped six times with a foot (three on one side followed by three on an orthogonal [right-angle] side). The ‘S’ test is then repeated and the mix is rated again.

Suitability of Segregation Tests

In the CMHA research (ref. 12); several mixes were used to determine the suitability of self-consolidating concrete segregation tests on the SCG mixes. Testing was performed to evaluate both the Column Technique for Static Segregation (ASTM C 1610) (ref. 19) and the European Sieve Segregation Test (ref. 20). It was found that these tests were not able to distinguish unstable SCG mixes from stable mixes. It is not clear if this was a function of the particular raw materials used or a general characteristic of coarse SCG mixes. The selfhealing (after agitation) test described above was found to be a much better indicator of stable and unstable mixes for SCG.

REFERENCES

  1. Specification for Masonry Structures, ACI 530.1-02/ASCE
    6-02/TMS 602-02. Reported by the Masonry Standards
    Joint Committee, 2002.
  2. Specification for Masonry Structures, ACI 530.1-05/ASCE
    6-05/TMS 602-05. Reported by the Masonry Standards
    Joint Committee, 2005.
  3. International Building Code 2003. International Code
    Council, 2003.
  4. International Building Code 2006. International Code
    Council, 2006.
  5. Specification for Masonry Structures, ACI 530.1-08/ASCE
    6-08/TMS 602-08. Reported by the Masonry Standards
    Joint Committee, 2008.
  6. Standard Specification for Aggregates for Masonry Grout,
    ASTM C 404-07. ASTM International, Inc., 2007.
  7. Standard Specification for Grout for Masonry, ASTM C
    476-07. ASTM International, Inc., 2007.
  8. Standard Specification for Concrete Aggregates, ASTM C
    33-03. ASTM International, Inc., 2003.
  9. Standard Specification for Aggregate for Masonry Mortar,
    ASTM C 144-04. ASTM International, Inc., 2004.
  10. Building Code Requirements for Masonry Structures, ACI
    530-08/ASCE 5-08/TMS 402-08. Reported by the Masonry
    Standards Joint Committee, 2008.
  11. Studies of Self-Compacting High Performance Concrete
    with High Volume Mineral Additives. Fang, W.;Jianxiong,
    C.; Changhui, Y., Proceedings of the First International
    RILEM Symposium on Self-Compacting Concrete, 1999,
    p. 569-578.
  12. Self-Consolidating Grout Investigation: Making and
    Testing Prototype SCG Mix Designs – Report of Phase
    II Research, MR31. Concrete Masonry & Hardscapes
    Association, 2006.
  13. Self-Consolidating Grout Investigation: Compressive
    Strength, Shear Bond, Consolidation and Flow – Report
    of Phase I Research, MR29. Concrete Masonry &
    Hardscapes Association, 2006.
  14. All-Weather Concrete Masonry Construction, TEK 03-01C,
    Concrete Masonry & Hardscapes Association, 2002.
  15. Standard Test Method for Sampling and Testing Grout,
    ASTM C 1019-07. ASTM International, Inc., 2007.
  16. Standard Test Method for Slump Flow of SelfConsolidating Concrete, ASTM C 1611/C 1611M-05.
    ASTM International, Inc., 2005.
  17. Grout for Concrete Masonry, TEK 09-04A, Concrete
    Masonry & Hardscapes Association, 2005.
  18. Standard Test Method for Slump of Hydraulic-Cement
    Concrete, ASTM C 143-05a. ASTM International, Inc.,
    2005.
  19. Standard Test Method for Static Segregation of SelfConsolidating Concrete Using Column Technique, ASTM
    C 1610/C 1610M-06. ASTM International, Inc., 2006.
  20. The European Guidelines for Self-Compacting Concrete:
    Specification, Production and Use. Self Compacting
    Concrete European Project Group, 2005.

Determining the Recycled Content of Concrete Masonry Products

  • August 2018

INTRODUCTION

Sustainable development has been defined as development that meets the needs of the present without compromising the ability of future generations to meet their own needs (ref.1). This is often expressed as a holistic approach to building design, with the goal of optimizing environmental, economic and social impacts, from site selection through building operation and maintenance. A sustainable building optimizes resource management and operational performance, while minimizing risks to human health and the environment. As such, providing a sustainable building project encompasses far-reaching design decisions, and recognizes the interrelationships between virtually all elements and phases of the project.

A range of products and programs has been developed to help designers achieve a more sustainable built environment. Whether in the form of design guidelines for particular building types, or rating systems that step the design team through a series of design considerations, all aim to provide practical guidance for achieving the almost overwhelming goal of sustainability.

Referenced and in some cases mandated by some branches of the Federal government, as well as many state and local governments, the United States Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED®) has become perhaps the most widely used of these programs in recent years. LEED is a voluntary rating system designed to provide guidance as well as national third-party certification for defining what constitutes a “green” building.

Concrete masonry building and hardscape products can make a significant contribution to meeting LEED certification. This contribution is augmented by the recycled content potential of the companion products necessary for a concrete masonry wall, such as grout, mortar and reinforcement products.

Concrete masonry building and hardscape materials can contribute to earning credits in several LEED categories, including Sustainable Sites, Energy and Atmosphere, Materials and Resources and Innovation in Design. More detail on LEED strategies incorporating concrete masonry and hardscape materials is available in TEK 06 09C, Concrete Masonry and Hardscape Products in LEED 2009 and PAV-TEC-016-16, Achieving LEED Credits with Segmental Concrete Pavement (refs. 2, 3).

LEED includes specific rating systems for various applications. The information in this TEK is applicable to LEED for new construction, school, retail, and core and shell development (refs. 4-7).

For these LEED programs, Materials and Resources Credit 4: Recycled Content allows up to two LEED certification points for using materials with recycled content. The inert nature of concrete masonry lends itself well to incorporating recycled materials as cement replacements, as aggregates and as other constituents in the concrete mix. This TEK provides guidance on determining the recycled content of concrete masonry products for the purpose of earning LEED credit under the new construction, school, retail, and core and shell development LEED programs.

The LEED for Homes (ref. 8) recycled content credit differs from these other programs. Concrete masonry walls are eligible for recycled content credit under the LEED for Homes Materials and Resources Credit 2: Environmentally Preferable Products, provided the masonry contains at least 25% recycled content (post-consumer plus one-half pre-consumer, as described in the following sections). Note, however, that the National Association of Home Builders with the International Code Council has developed their own green building standard that has similar requirements (ref. 9). See www.nahbgreen.org for more information.

USE OF RECYCLED MATERIALS IN CONCRETE MASONRY AND HARDSCAPE UNITS

When concrete masonry products incorporate recycled materials, due consideration must be given to ensure that the use of these materials does not adversely affect the quality or safety of the units or construction. Note that some recycled materials may only be regionally available. Designers should work closely with concrete masonry manufacturers to substantiate recycled content.

Unit Specifications

Whether produced using recycled or virgin materials, concrete masonry products are required to meet the applicable ASTM unit specification (see Table 1). These standards contain minimum requirements that assure properties necessary for quality performance. For example, many concrete masonry units are required to conform to ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units (ref. 11). ASTM C90 requirements include material requirements for aggregates, cementitious materials, and other constituent materials, physical requirements, finish and appearance requirements, and permissible variations in dimensions.

Aggregates, including recycled aggregates, for concrete masonry units are required to meet ASTM C33, Standard Specification for Concrete Aggregates, or C331, Standard Specification for Lightweight Aggregates for Concrete Masonry Units (refs. 19, 20), except that grading requirements do not have to be met. Aggregate characteristics governed include limits on deleterious substances and aggregate soundness.

Cements are required to meet ASTM C150 and supplemental cementitious materials such as fly ash must meet ASTM C618 (refs. 27, 28). In addition to cementitious materials and aggregates, the ASTM unit specifications also allow for the inclusion of “Other Constituents,” such as pigments, integral water repellents and finely ground silica. For a material to qualify for inclusion in a concrete masonry product under this provision, the material:

  • must have been previously established as suitable for use in the product, and
  • must either conform to applicable ASTM standards or be shown, via test or experience, not to be detrimental to the durability of the units or other masonry materials.

Fire Resistance Ratings

For construction requiring a fire resistance rating, the use of recycled aggregates may impact the method used to determine the hourly rating, because concrete masonry fire resistance ratings vary with the aggregate type(s) used to manufacture the units. Concrete masonry fire ratings can be determined by: model building code prescriptive tables (ref. 21), a standard calculation method as provided in Section 721 of the International Building Code (IBC) (ref. 21) and the ACI/TMS 216 (ref. 22); testing in accordance with ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials (ref. 23); commercial listing services; and deemed-to comply assemblies included in some building codes. These tools also include ways to increase a wall system’s fire resistance rating through careful placement of additional materials.

Currently, the standard calculation procedure applies to the following aggregate types: expanded slag, pumice, expanded clay, expanded shale, expanded slate, limestone, cinders, aircooled slag, calcareous gravel, and siliceous gravel. When units are made with a combination of these aggregates, the fire rating is determined by interpolation (see ref. 23 for more detail). When aggregate types other than those listed above are used, the fire resistance rating is determined using a method other than the standard calculation procedure.

TEK 07-01D, Fire Resistance Rating of Concrete Masonry Assemblies (ref. 24) contains a detailed discussion of concrete masonry fire ratings. Additional considerations for recycled aggregates which are not listed in the standard calculation procedure are their stability, safety and load-carrying ability when subjected to fire.

LEED MATERIALS & RESOURCES CREDIT 4: RECYCLED CONTENT

By increasing the demand for products that incorporate recycled materials, the Recycled Content credits are intended to reduce the environmental and societal impacts associated with extracting and processing virgin materials.

LEED awards 1 point to projects that demonstrate that the total amount of a project’s recycled content exceeds 10% based on both weight and the total building product costs. An additional point is awarded if the recycled content reaches 20%. Also, if the recycled content reaches 30%, a third point can be earned as an Innovation & Design credit.

LEED refers to the International Organization for Standardization (ISO) for the definition of what constitutes recycled content, and for the basis of determining the percentage – i.e., weight (ref. 25). Recycled materials are those materials diverted from the solid waste stream, either during the manufacturing process (pre-consumer) or after their intended use (post-consumer). The recycled content for LEED credit is determined as the sum of all post-consumer recycled content plus one-half of the pre-consumer recycled content.

To claim this credit, the LEED NC Reference Guide suggests establishing a project goal for recycled content materials, and dentifying product suppliers who can achieve this goal. The following sections describe how concrete masonry and hardscape products can contribute to recycled content goals.

Pre-Consumer Recycled Content

Pre-consumer (post-industrial) content as defined by the LEED v2.2 reference manual is “material diverted from the waste stream during the manufacturing process. Excluded is reutilization of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it (Source ISO 14021). Examples in the pre-consumer category include planer shavings, plytrim, sawdust, chips, bagasse, sunflower seed hulls, walnut shells, culls, trimmed materials, print overruns, over-issue publications, and obsolete inventories.” (refs. 4, 25) It is important for the producer to work with the material suppliers to determine which materials can be considered recycled and which cannot. It is important for the producer to have documentation from the material supplier stating that a material is considered recycled for the purposes of contributing to LEED certification.

Post-Consumer Recycled Content

Post-consumer recycled content is consumer waste that can no longer be used for its intended purpose. The official LEED definition of a post-consumer material is “material generated by households or by commercial, industrial and institutional facilities in their role as end users of the product which can no longer be used for its intended purpose. This includes returns of materials from the distribution chain (ref. 26). Examples of materials in this category include construction and demolition debris, materials collected through curbside and drop off recycling programs, broken pallets (if from a pallet refurbishing company, not a pallet-making company), discarded products (e.g. furniture, cabinetry and decking) and urban maintenance waste (leaves, grass clippings, tree trimmings, etc.) (refs. 4, 25).

As with pre-consumer materials, a producer should work with the material supplier to document that the materials being used are specifically documented as post-consumer recycled material for the purposes of contributing to LEED certification.

DETERMINING RECYCLED CONTENT

The LEED recycled content credit(s) is based on the recycled content percentages, based on the total value of all permanently installed materials on the project. Note that mechanical, electrical and plumbing components are excluded from this total, as are specialty items such as elevators. In determining the percentages of recycled content, the contribution from concrete masonry and hardscape products is added to the contribution from other building components.

The following sections describe the procedure for determining the recycled content of a particular product, then combining all such data to determine the overall recycled content percentage for the project. The percentages are based on both weight and cost, as described below.

For a Product

The producer is responsible for reporting the percentages of reconsumer and post-consumer recycled content for each product sold. If the producer supplies other products in addition to block such as reinforcement, mortar, etc., the producer should also document the recycled percentages in each of these products and report them to the contractor who purchased them.

The percentages are based on weight, as follows:

As an aid to the producer, CMHA has developed a simple spreadsheet to calculate these percentages (see Figure 1). Figure 1 illustrates the process of determining the weights of all constituent materials; determining the total weight; then determining the percent by weight of each recycled material. The total pre-consumer and post consumer percentages are simply the sum of the individual material percentages in each category.

Note that Figure 1 includes an alternate calculation, applicable to concrete products only. This alternate calculation is described below.

For a Product: Alternate Calculation per LEED for New Construction and Major Renovations

LEED for New Construction and Major Renovations, Version 2.2 and the LEED Reference Guide for Green Building Design and Construction, 2009 Edition (ref. 5, 26) provide an alternate method to calculate and report the recycled content for concrete products that use supplementary cementitious materials (SCMs), such as fly ash or ground blast furnace slag cement. This alternate method allows the recycled content calculation to be based on only the cementitious materials, rather than on all materials in the concrete mix. This alternate method helps offset the fact that the recycled content calculation is based on weight, and SCMs are typically very low in weight. For concrete mixes with SCMs as the only recycled content, this alternate method will result in a higher recycled content value than the conventional approach. For concrete mixes that incorporate both SCMs and other recycled materials, the manufacturer may want to evaluate the percent recycled content using both methods to determine which method yields the best result.

The basic calculation is the same as that described in the previous section, except:

  • when determining the percent post-consumer and percent pre consumer recycled content, divide by the total weight of the cementitious materials only, and
  • when determining the recycled content value, multiply the percent recycled content by the total value of the cementitious materials only.

Use of the alternative calculation method requires that the value of the cementitious materials be used in place of the total value of the product when the LEED project team determines the value of the recycled content. The producer would likely benefit from describing this value as a percentage of the value of the whole product and not as a monetary figure. When requested, the producer should report this value to the direct customer and not to a third party.

For the Project as a Whole

Based on information from the product suppliers, the design team determines the recycled content value for the project as a whole as follows:

  1. For each product, the percent recycled content is determined as the percent post-consumer (reported by the supplier) plus one-half of the percent pre-consumer. For the example in Figure 1, the percent recycled content for the concrete masonry units is 17.9% + 1/2(37.1%) = 36.5%
  2. For each product, the recycled content value is determined as the percent recycled content multiplied by the total product cost for the project. For the hypothetical project referenced in Figure 1, if the total cost of the concrete masonry units is $90,000, the recycled content value of the concrete masonry units is 0.365($90,000) = $32,805. It is important to note that the cost used in this calculation is the amount paid to the producer or the contractor for the product. It is not the cost of the individual materials that constitute the concrete masonry or hardscape product. The product cost should be supplied by the contractor. It is the contractor’s responsibility to separate their labor charges from the material charges.
  3. For the project as a whole, the recycled content percentage is determined as the sum of the recycled content values of each product, divided by the total cost of all of these products. If this total recycled content percentage is 10% or higher, the project earns one LEED point; if it is 20% or higher the project earns two LEED points. Projects with recycled content percentages of 30% or more may be eligible for an additional Innovation in Design point.

CONCRETE MASONRY UNITS RETURNED FROM A JOB SITE

Unused concrete masonry units returned to the manufacturer from a job site are considered under Materials and Resources Credit 2: Construction Waste Management. Under Credit 2, the building project with unused materials can earn LEED point(s) for returning those materials, and hence diverting them from a landfill. If subsequently used on another project, the recycled content of the units as manufactured is reported to the contractor or design team, as for unused concrete masonry products.

REFERENCES

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