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60 Applicability to Highway Practice The data obtained in this work have been used to develop recommended changes to current cement specifications and to recommend a test protocol that will allow producers to certify that cements containing processing additions are fit for the desired purpose. Construction of highway pavements using slipforming is an activity that is sensitive to the performance of the concrete mixture, probably to a greater extent than any other struc- tural system. The mixture is generally stiff, but it is essen- tial that workability be retained during the time from mixing to final placing and consolidation. Loss of workability will re- sult in poorly consolidated concrete, likely with a poor-quality surface. An additional complication is that entraining air is harder to achieve in low-slump mixtures, meaning that small changes in cementitious composition may have a significant influence on the air-void system, leading to potential loss of durability. Pavement slabs also have a large surface-to-volume ratio and the top surface is that which is directly exposed to loading and the environment, including deicing salt appli- cation. Durability is, therefore, a critical aspect of concrete pavement construction and loss of durability would be of great concern. The test data have shown that the primary effects of pro- cessing additions are reflected primarily in paste and mortar tests that are not necessarily observed in concrete. This is con- sistent with previously reported observations. Both fresh and early hardened properties of pastes and mortars were in the list of properties observed to be influenced by the use of pro- cessing additions. However, concrete mixtures appear to be largely unaffected by processing additions. Conclusions In general, processing additions at low dosages do not have a large influence on the performance of cementitious systems. For dosages of all inorganic materials of less than 1%, no significant effects were observed in the tests conducted. Based on this, it is recommended that, for inorganic PA dosages less than 1%, no additional testing is required above that required of the AASHTO M 85 cement specification. If the base cementitious system is close to the limits for a given parameter, then there is a possibility that inclusion of a PA may increase scatter in the test and/or increase the risk that the system may fail when tested. For this reason, it is rec- ommended that, for dosages of PA greater than 1%, a suite of tests be conducted on the system in compliance with the re- quirements of a protocol attached. In order to address con- cerns, and as supported by the test data, some additional tests are recommended for inclusion in the protocol. Laboratory tests were conducted on PA dosages up to and just above maximum limits imposed by existing cement spec- ification limitations on loss-on-ignition and insoluble residue. These would appear to limit maximum dosages of the mate- rials tested to between 3 and 8%, except for slag, which was not limited by this approach. A maximum dosage of any process- ing addition of 5.0% by mass of cement has been selected based on global practice. The data indicated that LS clinker appeared to be involved in affected systems slightly more than the other clinkers; C Ash and F Ash were more likely to be involved than slag or plain systems; and cement kiln dust was much more likely involved than the other processing additions. Caution should therefore be applied with the use of cement kiln dust and similar materials as processing additions. The parameters that appeared to be most sensitive to changing cementitious systems were shrinkage, ASR, and 28-day strength. No synergistic effects or interactions were observed with use of processing additions in systems containing supplementary cementitious systems. A draft protocol has been prepared, along with a modified version of AASHTO M 85; these are attached. C H A P T E R 6 Conclusions and Recommended Research
61 Future Work and Recommended Research A new protocol is provided as an attachment to this re- port in AASHTO format. Implementation of this protocol should take the form of adopting and referencing this pro- tocol in cement specifications. Education modules should also be prepared and presented to cement manufacturers, test laboratories, and specifying authorities so that the im- plications and details of the protocol are understood by the relevant personnel. Additional work that is required includes the need to ⢠Keep working on tests that can quantify the amount of processing addition in a given cement sample, parti- cularly for blind samples in which the type of PA is unknown. ⢠Monitor the performance of systems constructed in the field, possibly built using âfailingâ materials, to assess the sensitivity of field concrete to the changes detected in the paste and mortar tests. This work should also review whether or not the selected limits in the protocol are appropriate. ⢠Develop statistical approaches to setting and applying limits to the various test methods. At present, compressive strength is specified based on statistical approaches, but no other test method is approached in this way. Work is needed to develop approaches to addressing any test result that narrowly fails (or passes) a given test result.
