Quality of Prepackaged Powdered Materials Used in Construction What can be done to improve it? By Peter H. Emmons, Fred R. Goodwin, and Michael M. Sprinkel

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repackaged, dry, combined materials are commonly used as mortar, concrete, or grout in many construction and repair projects. In the United States alone, millions of bags are produced annually. But users of these materials are experiencing a number of quality issues that are impacting their projects. These issues include large variations in bag weights, which can affect the water-binder ratio (w/b), setting and curing times, and physical properties of a final product; segregation of components before and during mixing and placement; and material inconsistencies and contamination (for example, unwanted chlorides inadvertently added to the cement) that affect mechanical and durability properties. On September 4, 2013, users and manufacturers of prepackaged dry mixtures met in Indianapolis, IN, to participate in a workshop titled, “Establishing Standards of Care for Prepackaged Powdered Materials for Use in Construction,” organized by the Strategic Development Council (SDC), a council of the ACI Foundation. The goal of this workshop was to gain understanding of the issues regarding these materials and how they impact the industry, as well as to establish possible ways to improve the quality of prepackaged mixtures.

Background

Prepackaged concrete mixtures became available on the market in 19351 to provide homeowners with small quantities of materials needed for do-it-yourself (DIY) projects. Since then, the uses of these materials have been extended to contractors, Departments of Transportation (DOTs), and service companies (for example telephone, natural gas, and water utilities) for installation, construction, and repair projects. Key applications of prepackaged dry mixtures include placements where use of ready mixed concrete is restricted by rapid setting or long transit times,

dispersion of “difficult” ingredients (such as fibers or silica fume), small-volume placements, difficult access, complex formulations for synergistic effects, and performance and propriety specifications. Dry prepackaged mixtures once contained only cement and aggregates. Today’s mixtures may include more than 20 ingredients such as: sand (a blend of 1 to 5 sizes); binder (hydraulic cement and other cementitious materials); admixtures (accelerator/retarder, shrinkage-compensating admixtures, rheology-control additives such as high-range water-reducing admixture/thickener, and/or air-entraining admixture/defoamer); polymers; and fibers.

Things That Can Go Wrong

Concerns regarding dry prepackaged mixtures relate to manufacturing processes and field performance. Manufacturing processes As prepackaged dry materials have evolved to include more constituents, the potential for production issues has also increased. The main problems encountered during manufacturing include: contamination, segregation, variations in weights, sampling inconsistencies, and excessive storage times (that is, exceeding shelf lives for some constituents or of the final product). Contamination of dry prepackaged mixtures can occur during every operation, including: Extraction or production of constituent materials; Shipping, handling, and storage of constituent materials; and Production, packaging, shipping, and storage of final products. Contamination can be caused by improper cleanout of equipment between deliveries or batches (raw material trucks, dry material mixers, and bagging line equipment

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must be regularly inspected and cleaned); improper inventory control (for example, taking delivery of the wrong materials or storing material in the wrong silo); poor maintenance, which can lead to leakage of materials between silos, moisture contamination, or incomplete shutoff of gates during material transfers; or additives in bulk bags. Segregation is a change in the material composition based on size, density, or shape of particles. In prepackaged dry mixtures, segregation can take place during storage, discharge of dry materials from silos, mixing operations, or bagging operations. Segregation can also occur once the product is mixed with liquid, as differences in densities can cause heavier aggregates to settle to the bottom and lighter components, such as water and fine particles, to rise to the surface of the mixing container. Weight variations for bagged materials can result from inadequate calibration of the packaging weighing system or filling system issues that can cause materials to “hang up” in the chute or hopper. It usually takes only 3 to 5 minutes to batch, mix, and pack about 3000 lb (1361 kg) of dry materials at a modern plant. Therefore, not every produced batch can be tested. Collected samples might come from a location in the process before final packaging and/or be contaminated and thus not representative of the final product. The sample may test falsely positive (appears to be good but represents a bad batch) or falsely negative (appears to be bad but represents a good batch). Grab samples are a snapshot of what happened at one point of the process, while composite samples give an average overview of what the production campaign looks like (but may blend out wide fluctuations from batch to batch). The sample itself may be also segregated (not homogenous), so the tested product is not the same as the final product. For prepackaged dry mixtures, the raw materials and the finished products can have limited shelf lives, and these will be controlled by moisture absorption, carbonation, and lumping. The latter can be influenced by the introduction of moisture during processing or packaging, the permeability of packaging materials, and the humidity and temperature conditions for the raw material and finished-product storage facilities. Field performance Faults in manufacturing of prepackaged dry mixtures, if present, will contribute to problems in the performance of those products in the field. The main concerns that have been observed on construction or repair projects include: Inconsistent package (bag or sack) weights; Variations in composition;

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of components during mixing and place•• Segregation ment; and contamination. •• Material Non-uniformity in package weights (Fig. 1) causes

uncertainty during batching and can increase the need for onsite quality assurance (QA). The packaging or specification will normally call for a fixed water addition based on the packaging unit, rather than on field measurement of the dry material weight. If the package weight varies, the admixture dosage rates and w/b will vary. As a result, the fresh properties of mixtures (including flow, consolidation effort, density, setting time, and bleeding) and the hardened properties (including volume stability, strength, permeability, and durability) will be inconsistent. As seen in Fig. 2, the cement factor can fluctuate for prepackaged high-performance grout mixtures, even if they

Fig. 1: Bag weights measured for two different lots of a prepackaged grout product. The number 50 in the red box marks the net mass stated on the package (illustration courtesy of Structural Technologies)

Fig. 2: Cement factor variation of the same prepackaged grout product mentioned in Fig. 1 (illustration courtesy of Structural Technologies) (Note: Cement factor calculated by

sieving out the sand)

are from the same lot. There have also been reports that portland cement may be extended with fly ash or other cementitious material without any notification on the package. Variations in binder composition are highly likely to affect fresh and hardened properties of the installed product. When prepackaged dry materials are delivered with less than the weight indicated on the packaging, the w/b will be higher than recommended and segregation of components will occur when mixing water is added. The resulting excessive bleeding (Fig. 3) can produce zones of wet, soft grout (Fig. 4) in post-tensioning installations. Contaminates such as wood chips (Fig. 5) or chlorides may result in undesirable field performance. For example, one manufacturer of post-tensioning (PT) grout released a product with cement contaminated with chlorides over a 10-year period. The contamination went unnoticed until Texas DOT was conducting a post-grouting inspection for voids in the end cap areas of bridge pier bents. The inspectors found soft grout, and subsequent tests of the soft grout and other grout in the bents revealed high chloride contents.2 As of June 25, 2013, according to the Federal Highway Administration website, 35 bridges in the United States have been identified with possible elevated chlorides in PT grout (www.fhwa.dot.gov/bridge/120210.cfm). Because chloride contamination may cause corrosion of tendons, the contamination could result in significant reductions of the service lives of the listed bridges.

Fig. 3: Evidence of segregation observed for two different prepackaged high-performance grouts. After mixing the prepackaged dry materials with the amount of water for w/b values of 0.65, the grouts were placed in 4 x 8 in. (100 x 200 mm) cylinder molds. Cylinder 1 exhibits a thick layer of weak foam grout and Cylinder 2 exhibits a layer of soft grout that had been covered by about 1.5 in. (64 mm) of bleed water before mold removal (photo courtesy of Virginia Center for Innovation & Research)

Relevant Documents

Standards and specifications Depending on the material application, ASTM International publishes three specifications for packaged dry materials: ASTM C387/C387M-11b, “Standard Specification for Packaged, Dry, Combined Materials for Concrete and High Strength Mortar,” covers four types of concrete (high-early strength, normal strength, lightweight normal strength, lightweight normal strength with normalweight sand) and high-strength mortar; ASTM C928/C928M-09, “Standard Specification for Packaged, Dry, Rapid-Hardening Cementitious Materials for Concrete Repairs,” deals with cementitious mortar or concrete materials for rapid repairs to hardened concrete pavements and structures; and ASTM C1107/C1107M-13, “Standard Specification for Packaged Dry, Hydraulic-Cement Grout (Nonshrink),” covers non-shrink hydraulic grout. Prepackaged dry concrete and mortar mixtures conforming to ASTM C387/C387M have to meet all physical requirements included in the specification. All packages have to be identified as ASTM C387/C387M compliant and include markings for material type, net mass, yield, and amount of mixing water recommended for a concrete slump of 2 to 3 in. (50 to 75 mm) or a mortar flow of 110 ± 5%.

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Fig. 4: Wet and soft grout that formed during an inclined tube test. This result, which is caused by excessive bleeding, indicates that the grout could allow corrosion of post-tensioning strands if used in the field (photo courtesy of Structural Technologies)

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Fig. 5: Wood chips found in a prepackaged grout were determined to be the result of contamination of a load of silica fume used during the manufacturing process (photo courtesy of Structural Technologies) Concrete international april 2014

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Prepackaged dry repair mixtures meeting the requirements of ASTM C928/C928M must have their specification designation marked on each package, as well as the material’s packing date, yield, and net weight. In addition, as stated in ASTM C928/C928M: “The contents of any container shall not vary by more than 2% from the weight stated in the markings. The average weight of filled containers in a lot shall be not less than the weight stated in the markings.” Product markings for ASTM C1107/C1107M prepackaged dry grout are required to include net weight, date of manufacture (including recommended use expiration date), lot identification number, and yield at either the maximum water content or maximum consistency. Per ASTM C1107/C1107M: “The yield claimed shall not be greater than that measured.” The Post-Tensioning Institute regulates PT grout with the third edition of “Specification for Grouting of PostTensioned Structures (PTI M55.1-12).” This edition includes modifications to the previous version of the wick-induced bleed test, a new test to identify grouts that are susceptible to bleeding and segregation (the EN 445 inclined tube test), and modifications to the definition of the limiting chloride ion content within grout. ACI 562-133 also incorporates requirements for material testing, inspection, and test frequencies for repair materials. The document directs the licensed design professional to include these requirements in the contract documents. ACI 546.3R4 and ICRI 320.2R5 are suggested for guidance.

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Guides and guidelines Several documents deal with selection and data sheets for prepackaged repair materials. They include ACI 546.3R-06,4 ACI 364.3R-09,6 and ICRI 320.3R-2012.7 ACI 546.3R provides guidance on repair material selection by identifying common repair materials, discusses material properties and test procedures for measuring these properties, recommends minimum test values or performance levels, and discusses the importance of material properties for various applications and service environments. ACI 364.3R and ICRI 320.3R are intended to serve as guides for preparing repair material data sheets. According to both documents, such data sheets should include information on recommended use, claimed benefits, and stated limitations as well as material properties (composition and physical and hardened properties), packaging and storage, and safety information. All reported data should also include test methods used for their determination.

Quality Control and Quality Assurance

Despite the existence of the listed standards, specifications, and guides, the quality control methods used by many manufacturers of prepackaged dry mixtures appear to be inadequate. Quite often, to avoid complications, users of these materials have to rely on their internal QA and testing protocols to evaluate materials for each specific project. It’s apparent that manufacturers and specifiers of prepackaged dry mixtures do not support data sheet protocols, since these protocols are not required by existing product specifications. While data sheet protocols would incur additional costs related to testing and education on the use of the provided data, the protocols would not guarantee increased sales. Specifiers are apparently concerned with the effects of having limited quantities of compliant materials, the additional material costs that would passed on to the owners, as well as the need for education on the applicability of the data contained in the data sheet protocols.

What’s Next?

Participants of the SDC workshop on prepackaged dry mixtures identified quality and performance issues with these materials and proposed solutions to overcome them. Recommendations for critical actions and solutions to improve field performance of prepackaged dry materials include: Minimizing materials variability through implementation of uniformity standards; Standardizing bag weight tolerances; Requiring proper labeling of products’ shelf lives and storage requirements; and Addressing bleeding and segregation of mixtures prepared from these materials. These actions/solutions can be realized through development of: QC and QA procedures for manufacturers, specifiers, and owners to ensure consistency of products, with

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clearly defined required tests (transparent, repeatable, and reproducible*); frequency and depth of testing; and standardized data sheet protocols; Plant certification program for grout and repair material manufacturers; and Performance-based requirements and specifications.

•• •*Transparent • tests are published in sufficient detail that similar results can be produced by independent agencies from the producer. Repeatable tests statistically demonstrate that retesting of the same material can be duplicated within a given precision. Reproducible tests statistically demonstrate that values similar to published or previous test values can be obtained from a different testing agency.

Workshop participants agreed that the SDC should form a new Working Group to address these and other issues with prepackaged dry materials. This group would communicate the urgency of the matter within the SDC, with the goal of defining prepackaged dry materials as an Industry Critical Technology (ICT). The ICT champion would then, with the support of SDC’s resources, play a direct role in working with all interested parties toward improvement and assurance of quality of the prepackaged dry materials. Acknowledgments The authors would like to thank John R. Crigler of VStructural (VSL), Kevin MacDonald of Beton Consulting Engineers, Richard F. Heitzmann of Structural Technologies, and Theodore L. Neff of the Post-Tensioning Institute for sharing their expertise on the subject.

References

1. “Significance of Tests and Properties of Concrete & ConcreteMaking Materials,” STP169D, J.F. Lamond and J.H. Pielert, eds., ASTM International, West Conshohocken, PA, 2009, 664 pp. 2. Merrill, B., “Memorandum Carbon Plant Road,” Texas Department of Transportation, Austin, TX, Sept. 14, 2010. 3. ACI Committee 562, “Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings (ACI 562-13) and Commentary,” American Concrete Institute, Farmington Hills, MI, 2013, 59 pp. 4. ACI Committee 546, “Guide for the Selection of Materials for the Repair of Concrete (ACI 546.3R-06),” American Concrete Institute, Farmington Hills, MI, 2006, 34 pp. 5. Guideline No. 320.2R-09 (formerly No. 03733), “Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces,” International Concrete Repair Institute, Rosemont, IL, 2009, 36 pp. 6. ACI Committee 364, “Guide for Cementitious Repair Material Data Sheet (ACI 364.3R-09),” American Concrete Institute, Farmington Hills, MI, 2009, 12 pp. 7. Guideline No. 320.3R-2012, “Guideline for Inorganic Repair Material Data Sheet Protocol,” International Concrete Repair Institute, Rosemont, IL, 2012, 9 pp. Note: Additional information on the ASTM standards discussed in this article can be found at www.astm.org. Selected for reader interest by the editors.

Peter H. Emmons, FACI, is CEO of Structural Group, Baltimore, MD. He is a member of ACI Committees 364, Rehabilitation; 546, Repair of Concrete; 562, Evaluation, Repair, and Rehabilitation of Concrete Buildings; 563, Specifications for Repair of Structural Concrete in Buildings; and E706, Concrete Repair Education; as well as a SDC and Concrete Research Council industry partner. He received the ACI Wason Medal for Most Meritorious Paper in 1996, the ACI Arthur R. Anderson Award in 2000, and the ACI Roger H. Corbetta Concrete Constructor Award in 2009. His company received the ACI Charles S. Whitney Medal in 2006. He is Past President and a Fellow of ICRI and the author of Concrete Repair and Maintenance, Illustrated. Fred R. Goodwin, FACI, is a Fellow Scientist with over 30 years of experience in the construction chemicals industry, including cement manufacture, research, development, and technical support of grouts, adhesives, coatings, shotcrete, flooring, and concrete repair materials. He has been with BASF and its predecessors for 24 years. He received the ACI Delmar Bloem Award in 2011. He is a member of the ACI Technical Activities Committee (TAC) and Chair of ACI Committee 515, Protective Systems for Concrete. He is a Fellow of ICRI and Chair of the ICRI TAC, as well as an Honorary Member of ASTM International Committees C01, Cement, and C09, Concrete and Concrete Aggregates; and Chair of Subcommittee C09.41, Hydraulic Cement Grouts. Michael M. Sprinkel, FACI, is Associate Director at the Virginia Center for Transportation Innovation and Research (VCTIR), Charlottesville, VA, where he has served in various research positions since 1972. He received the ACI Robert E. Philleo Award for outstanding lifetime contributions in concrete materials in 2012. He is past Chair of ACI Committee 503, Adhesives for Concrete, and 345, Concrete Bridge Construction, Maintenance and Repair; and a member of 546, Repair of Concrete; 548, Polymers and Adhesives for Concrete; the Technical Activities Committee (TAC); and Chair of the TAC Construction Standards Committee. He is past Chairman of Transportation Research Board (TRB) Committee AFN00, Section-Concrete Materials; Member Emeritus of Committee AFN20, Properties of Concrete; past Chair of TRB Committees AFN20, Properties of Concrete; and AHD40, Polymer Concretes, Adhesives, and Sealers. He is also a Fellow of the American Society of Civil Engineers.

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