Research Projects

Implementation of Performance based Approach based on Emerging Test Methods to Formulate ASR Resistant Concrete Mixes

Based on extensive research supported by TxDOT and Bureau of Reclamation, two ASR test methods (i.e., a rapid aggregate chemical test called VCMD and an accelerated concrete cylinder test - ACCT) and a combined innovative approach with four recommended steps were developed for formulating performance-based alkali-silica reaction (ASR)–resistant concrete mixes. This performance based approach has a great potential to formulate ASR resistant concrete using locally available aggregates and SCMs.

Background (Describe the current situation or problem in the industry, and how your idea would address it.)

Based on extensive research supported by TxDOT, two ASR test methods (i.e., a rapid aggregate chemical test and an accelerated concrete cylinder test) and a combined innovative approach with four recommended steps were developed for formulating performance-based alkali-silica reaction (ASR)–resistant concrete mixes. The approach includes determination of aggregate reactivity and threshold alkalinity (THA) using the VCMD method (Step 1) followed by formulation of ASR resistant concrete mixes (Step 2), mix design verification (Step 3) based on the THA and pore solution alkalinity (PSA) relationship and finally mix design validation using the ACCT method (Step 4).Guidelines on utilization of the four steps depending on the need of testing duration and reliability were also developed. The approach has been validated through extensive laboratory testing and currently being employed to validate the commonly used Texas precast mixes.

Objective (What is the desired product or result that will help the airport industry?)

The objective of the proposed study is to implement the developed approach using commonly used aggregates as well as aggregates with high source variability and potential new aggregate sources and validate if the current mix design practices are adequate to prevent ASR. The combined approach based on rapid and reliable test methods will facilitate formulating (a) case-specific ASR-resistant mixes (tailoring mix design depending on the level of protection needed) using locally available materials to ensure long-lasting durable concrete and save on repair costs, and (b) an effective and safe way to use locally available fly ashes (the ACCT method has the capability to perform fly ash optimization effectively) and meet future challenges when good-quality fly ashes are no longer available.

Approach (Describe in general terms the steps you think are needed to achieve the objective.)

Steps 1: Measure the reactivity and threshold alkali loading (TAL) commonly used aggregates for making concrete for the major airports using the VCMD method. The VCMD method is published a full standard in AASHTO (T364). It takes around 5 days to determine reactivity and around 20 days to determine TAL. The reactivity using conventional methods (ASTM C 1260, MCPT, ASTM C 1293 and petrographic techniques) will also be measured for comparison and justify/highlight the advantages / reliability of the VCMD method. The VCMD was found to be very effective to use in place of ASTM C 1260 (alternative to C 1260) and consistently identified the aggregates belong to false positive and negative categories.
Step 2: Development of an ASR-resistant mix by applying suitable mix design controls depending on VCMD based reactivity prediction, TAL, and some consideration on the severity of exposure conditions.
Step 3: Mix design adjustment/verification based on THA-pore solution alkalinity (PSA) relationship (optional but recommended): Determination of PSA of the mixes in Step 2 using the pore solution extraction method. If the extraction method is not available, a combined use of the NIST model (estimating PSA contribution from cement portion) and ASTM C311 (determining available alkalis from supplementary cementitious material [SCM] used) was found to be effective to estimate PSA of the cement-SCM combination with acceptable accuracy; PSA needs to be below THA to prevent/minimize ASR.

Step 4. Mix design validation through concrete testing – use of the ACCT method to measure ASR expansion of concrete mixture after Step 2/3 over time in a relatively short time (45–75 days).

All mix design Steps 1 to 4 are recommended to develop ASR resistant case specific mixes (performance based) with the highest reliability and fine tuning the current mix design practices. If a strong agreement between mixes developed through Steps 1–3 and validation testing in Step 4 is observed, then requirement of concrete validation testing (Step 4) can be considered as optional. Determination of aggregate reactivity using the ACCT method in a relatively short time (28–45 days) followed by mix design formulation in accordance with AASHTO R80-17/ASTM C1778 is recommended as an effective option. As the ACCT method measures aggregate reactivity with high reliability, it ensures effective utilization of the guidelines provided in the current practices (AASHTO R80-17/ASTM C1778) and formulate safe ASR resistant mixes. The ACCT method can be used to test field concrete mixes. Job concrete mixes formulated based on entirely the current practices (e.g., in accordance with AASHTO R80-17/ASTM C1778) can be validated using the ACCT method. This option is recommended when the aggregate reactivity prediction based on the current test methods (e.g., ASTM C1260 and ASTM C1293) seems to be satisfactory.

The full-scale characterization of fly ashes and other SCMS will be conducted using QXRD (evaluation of type and content of crystalline phases and amorphous content), soluble available alkalis (ASTM C311), pore solution chemistry along with determination of parameters by the conventional ASTM C618. A favorable comparison between characteristic chemical and mineralogical parameters of the fly ashes and ACCT based ASR performance prediction has been observed. This combined innovative approach was found to be effective to test the effectiveness (optimization) of different types of fly ashes to prevent ASR in a rapid (within 75 days) and reliable manner and formulate case specific performance-based ASR resistant concrete mixtures using locally available fly ashes.

Cost Estimate and Backup (Provide a cost estimate and support for how you arrived at the estimate.)

This should be a minimum of 2.0-2.5 years study with $160,000.00 per year.

Related Research - List related ACRP and other industry research; describe gaps (see link to Research Roadmaps above), and describe how your idea would address these gaps. This is a critical element of a synthesis topic submission.

The current approach of predicting aggregate reactivity and preventing damaging ASR in fresh concrete heavily depends on accelerated mortar-bar tests (AMBTs) [e.g., ASTM C1260/1567] and concrete prism test (CPT) [e.g., ASTM C1293]. AASHTO R80-17 provides a procedure for evaluating aggregate reactivity by ASTM C1260 and/or ASTM C1293 and determining measures to prevent ASR on the basis of performance testing or prescriptive selection from a list of different options. Although these approaches have resulted in significant advances in the avoidance of ASR damage in concrete structures, there were limitations and drawbacks. ASTM C1260 is a rapid test (14 days testing period) but reliability is questionable because of severity of test conditions and some limitations in the sample preparation. ASTM C1293 is accepted mostly as a reliable test method but long testing time (1-2 year) is a major drawback. A comparative assessment between ASTM C1260 and C1293 leads to generation of aggregates belong to false positive and negative categories followed by creating exclusion list (i.e., recommending not to use those aggregates) by many agencies. New cases of ASR are continuously being reported despite the advancement of the last decades. Therefore, the demand for developing rapid and reliable ASR test methods is high. The current practice is to assign a common relatively lower level of alkali loading (e.g., 2.1-2.4 kg/m3) for all concrete mixes irrespective of type of applications such as an example of one size fits for all. Fundamentally, the effective approach of designing ASR resistant mix relies on determining aggregate threshold alkali (THA) of ASR. The current ASR tests are not capable to determine aggregate THA and test the effects of cement alkalis on ASR. A reliable test along with performance based mix design approach will enable to allow locally available materials (e.g., marginal materials, aggregates in the exclusion list, recycled materials etc.) and promote sustainability in one hand and ensuring durable long lasting structures on the other hand. An effective way of tailoring mix design depending on the level of protection needed is warranted. This will ensure valuable resource conservation and avoid paying for premium ASR protection when only minor protection is needed. More specifically, Industry is looking for a test method or approach to test effectiveness of ASR resistance of field concrete mixtures before placement. No test(s) is currently available to test field concrete mixtures.



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Idea No. 197