Late last month, NRMCA Engineering Department staff traveled to Salt Lake City to attend the American Concrete Institute's Spring Convention. The following summarizes committee activity involving NRMCA Staff representation:
132 – Responsibilities – The committee is finalizing a Tech Note on the responsibilities associated with complying with requirements for strength test specimen initial curing at the jobsite. Colin Lobo maintains representation on ACI 132.
201 – Durability – Five tech notes are being developed: 1. Repair of structures affected by physical salt attack; 2. Recommendations for mitigating physical salt attack in new construction; 3. Joint deterioration due to deicers; 4. Iron sulfide (Pyrrhotite) in concrete; and 5. Microbial Induced Corrosion of Concrete. The committee discussed a proposal to allow a performance-based alternative to the w/cm requirement for Exposure Class C2 in ACI 318. A parallel ballot in 318A resulted in changes that were not supported by Committee 201. The committee has established task groups to develop guide specifications for: 1. Obtaining Durability in Design and 2. Executing Durable Concrete in Construction. The documents will be developed in a two-column format as specification and commentary. A task group on alkali aggregate reactions discussed that field exposure blocks were failing at 10 years and this was inconsistent with 2-year ASTM C1293 test results showing acceptable levels of SCMs to mitigate ASR. Mini sessions are planned on microbial induced corrosion for the next convention.
The committee is planning sessions for future conventions: 1 Microbial induced corrosion; 2. Quality assurance methods in the field for durability; 3. Health monitoring of structures for ASR; 4 Other sessions on AAR; 4. Constructability and durability requirements of concrete. The committee is collecting papers for two special issues of ACI Materials Journal on durability in 2019: one on Chlorides and Corrosion and another on SCMs. Karthik Obla maintains representation in ACI 201.
211 – Mixture Proportioning – The committee continues to work on revising its primary document on mixture proportioning ACI 211.1. A guide for selecting proportions for pumpable concrete has been completed. Task groups are developing documents on 3-point curves for trial batches, assessing aggregate gradations and aggregate packing models. Revisions to the document on proportioning with ground limestone and mineral fillers is being finalized. A technical session on “Specifications and ACI 211” is planned for a future convention. Karthik Obla maintains representation on ACI 211.
214 – Strength Tests – The committee is working on a revision to the 214R document. The draft will include guidance on percent within limit (PWL) specifications and will address determining target average values using statistical principles for specified flexural strength, rapid chloride permeability and elastic modulus. The document on core testing will address a process for considering a low core strength test from a set of three. Two tech notes are being developed; 1. Cylinder vs Cube strengths; 2. Using two instead of three 4x8 in. cylinders for acceptance testing. Karthik Obla maintains representation on ACI 214.
232 – Fly Ash – A revised version of the committee’s document is available: ACI 232.2R-18, Use of Fly Ash in Concrete. The committee has developed a Tech Note on Limits on the Quantity of Fly Ash in Concrete based on an NRMCA Specification in Practice topic and is working on another topic on Recovered Fly Ash. Karthik Obla is the vice chairman of this committee.
240 - Pozzolans – A Tech Note on pozzolans derived from ground glass is being worked on. The task group is investigating test methods for pozzolanic activity for natural pozzolans. It was reported that some natural pozzolans with high total alkali are effective in mitigating ASR. Total alkali content is a typical indicator for effective fly ash. A trade group representing suppliers of natural pozzolan reported that 500,000 tons of natural pozzolans were sold in the U.S. in 2017, primarily by three suppliers. Capacity additions are underway with plans for 5 million tons in 10 years. More information is available here. Karthik Obla maintains representation on ACI 240.
242 – Alternative Cements – The committee is working on two documents: a practitioner’s guide and a State of Art report on alternative cements. A “Roadmap to Implementation” will be disseminated through the ACI Strategic Development Council. The committee will develop Tech Notes on alkali activated cements, calcium sulfoaluminate cements and property-based cementitious materials such as rapid hardening cements.
301 – Specifications for Structural Concrete –The committee is working on revisions for the next version of ACI 301 scheduled to be published in 2020. Revisions currently in progress impact most sections of the specification and the committee spent most of its time on resolution to balloted revisions. Some approved revisions include clarification of duties and responsibilities of the owner’s and contractor’s testing agencies; removal of the minimum cement content for floors (this may be addressed in the section on industrial floor slabs); making adjustments to mixtures without a submittal to limits stated in the original submittal; revisions to the ASR requirements – test data limited to 24 months, options include report on aggregate reactivity by ASTM C1293; mitigation of ASR by ASTM C1567 with conditions, and limit on concrete alkalis based on aggregate reactivity; options for prequalification testing of self consolidating concrete; a limit on chlorides for concrete placed on stay-in-place galvanized forms; prequalification testing for modulus of elasticity, if specified; and some minor changes based on approved revisions to ACI 318. The committee will revise the specification as changes are approved to ACI 318. Colin Lobo maintains representation on ACI 301.
318 – Building Code for Structural Concrete – ACI 318 is scheduled to be published by the summer of 2019 for it to be referenced in the next edition of the International Building Code. Revisions must be approved in summer of 2018 followed by a review by ACI Technical Activities Committee. The revised ACI 318 will be available for public comment in early 2019. Comments from that process should be addressed before the new version is published. For concrete materials sections in Chapters 19 and 26, about 20 changes have been approved. Code changes approved at this convention include use of mineral fillers with restriction to concrete exposed to sulfates; and chloride limits based on cementitious materials (as opposed to cement). Other changes close to approval include details regarding pre-qualification testing for modulus of elasticity; alternative option for the more severe sulfate exposure; revising the “lambda” factor for design of lightweight concrete on the basis of density; including use of shotcrete; establishing an exposure condition where the designer should consider requirements for alkali aggregate reactions; prohibiting the use of recycled aggregate or alternative cements unless approved by the designer and other minor revisions. A proposal for a performance-based alternative to w/cm for exposure class C2 (exposure to external chlorides) was tabled due to lack of support on the details from Committee 201 on Durability. Colin Lobo maintains representation on ACI 318 and ACI 318 Subcommittee A.
325 – Concrete Pavements – NRMCA’s Brian Killingsworth maintains representation on ACI 325 on Concrete Pavements. The committee currently has four documents under development or revision. The committee is rewriting ACI 325.12R-02 (Reapproved 2014): Guide for Design of Jointed Concrete Pavements for Streets and Local Roads and is being be led by Killingsworth. Revisions to this document will be completed this spring and balloted in the fall. The committee is developing ACI 325.YR Report on Precast Concrete Pavements - State of the Practice which is based upon work completed by Tayabji for SHRP2. The committee developed ACI 325.14R.17 Guide for Design and Proportioning for Concrete Pavements which was published by ACI in 2017. A revision is underway of ACI 325.11R Accelerated Techniques for Concrete Paving. Work is nearly complete and will be published in the next few months. Work is also underway to update ACI 325.ZR: Design and Construction of Continuously Reinforced Concrete Pavements over the next few months. Lastly, ACI 325.13R-06: Concrete Overlays for Pavement Rehabilitation is being reviewed and updated. This work will continue over the next year. Killingsworth will ensure that considerations for streets and local roads will be included in all documents.
329 – Performance Criteria for Ready Mixed Concrete – Tech Note regarding the minimum cementitious materials content in specifications (based on NRMCA document) will be published soon. The committee continues to work on developing a Guide to Writing a Performance-Based Specification. The outline and format was discussed and finalized. A chapter will briefly discuss selected test methods and criteria for various performance attributes. The document will follow the MasterSpec format so that it can be effectively used by practicing engineers. Obla discussed a proposed performance alternative to w/cm for durability in ACI 318 working through ACI 201. Lobo discussed the test methods and criteria on the FHWA Performance Engineered Mixtures for Pavements, AASHTO provisional standard PP84, planned implementation efforts. Obla has finalized an article for Concrete International on case studies of performance-based projects based on a previous ACI convention session. Colin Lobo (secretary) and Karthik Obla maintain representation on Committee 329.
330 – Parking Lots – The ACI 330 Committee continues to work on revising its Guide document ACI 330R. Revisions to each chapter in the document is currently being balloted. General comments were addressed during the meeting. Specific comments will be addressed in the ballot. Amanda Hult maintains representation in ACI 330.
522- Pervious Concrete – All chapters for the ACI 522R guide document were balloted before the Spring 2018 meeting. The revised document will be sent to Technical Activities Committee for review and the committee will address its comments during the Fall 2018 meeting. Comments on the specification ACI 522.1-13 Specification were addressed during this meeting. At the next convention in Las Vegas, the student competition will involve pervious concrete. The committee is expecting 55-60 teams from 20 countries. Amanda Hult maintains representation in ACI 522.
555 – Recycled Materials – The committee is revising its document Removal and Reuse of Hardened Concrete to include a section on crushed concrete aggregates from returned concrete based on research work conducted at the NRMCA Research Laboratory. The committee organizes technical sessions on the use of recycled materials in concrete as there is continued interest on these topics. ACI University includes an on-demand course on Recycled Concrete. Karthik Obla maintains representation in ACI 555.
Other Information included:
• Karthik Obla delivered a presentation on the NRMCA Producer Quality Management System in a session on Quality Management.
• The Committee on Self Consolidating Concrete is developing a Tech Note on Influencing Factors and Models to Predict Formwork Pressure Exerted by SCC. SCC formwork can be designed to withstand 50-70% of the full hydrostatic pressure. Models estimate formwork pressure based on slump flow, T50 time and visual stability index (VSI) determined in accordance with ASTM C1611.
• A presentation reported the use of carbon nano-tubes to modify the stiffness of concrete by improving that of the aggregate/matrix interface and hydration products. Tests indicate an addition level of 0.015% by mass increased the modulus of elasticity by 50%.
• ACI Concrete Research Council (CRC) has selected potentially six project proposals for funding: three in materials and three in structures. Funding is at the level of $50,000 each. Projects should demonstrate benefit of their work to documents of ACI committees. A previously funded project is assimilating the variations on recommendations and requirements for durability in ACI committee documents and standards. The report will make recommendations to the impacted committees to harmonize guidance and requirements on durability in ACI Documents. Colin Lobo maintains representation on ACI CRC.
• Frank Kozeliski, a past NRMCA Board member and currently a consultant in New Mexico, was recognized with an honorary membership in ACI, its highest recognition.
For more information, contact Colin Lobo or Karthik Obla.
National Ready Mixed Concrete Association