Optimization of Mixture Proportions for Concrete Pavements—Influence of Supplementary Cementitious Materials, Paste Content and Aggregate Gradation

The ultimate goals of this study included investigation of the optimal ranges for paste content, amount of cementations materials and aggregate gradation for concrete paving mixtures. In general, the optimum concrete mixtures developed in this study contained low paste content (below 23%), and were characterized by low scaling and sorptivity. In addition, it was also possible to achieve high cement replacement levels for these mixtures. Finally, for optimized fly ash mixtures, the selection of well graded aggregate gradation with high packing density increased the most desired paste content for those mixtures, thus indicating that combined aggregate gradation has strong influence on concrete performance. Lastly, concrete mixtures developed with optimum ranges of variables studied in this research contained low cement content. The overall scope of the research was divided into three distinctive phases, each of which is described briefly below: PHASE I: This phase consisted of statistical optimization of the proportions of concrete binder. The Central Composite Design methodology (CCD) was used to design the experiment for the optimization of binder in three types of concrete mixtures: a) cement + fly ash, b) cement + GGBFS, and c) cement + fly ash + GGBFS. The variables studied in each of these systems included: paste content (from 21 to 25 % by mixture volume) and total content of supplementary cementitious material (SCM) in the mixture. This was expressed as weight percent of total binder, and varied depending on the binder system used. PHASE II: The main goal of this phase was to investigate the effect of different aggregate gradations on the fresh and hardened properties of optimized concrete mixtures developed in PHASE I, as well as to identify the most desired aggregate gradations for paving mixtures. Different aggregate gradations were prepared by blending of 2, 3 or 4 different sizes of aggregates based on concept of Shilstone’s Coarseness Factor Chart. PHASE III: The concept of air-free paste–aggregate void saturation ratio (k”) introduced in PHASE II seemed to fairly accurate link the properties of concrete mixtures with their paste content. Thus, it was decided to further investigate this concept in connection with aggregate packing density (Φ). In addition, it was believed that defining optimum values of “k” will allow for revising the paste content ranges developed in PHASE I for different systems, and thus define more general optimum paste ranges for paving mixtures

Updating Physical and Chemical Characteristics of Fly Ash for Use in Concrete

When incorporated in concrete mixtures, fly ashes are known to influence both its fresh and hardened properties. An accurate and quick technique to predict the extent of this influence based on the characteristics of fly ash would be highly beneficial in terms of field applications. The current study was an attempt to quantify the effects of fly ashes on the properties of pastes as a function of: (a) the mean particle size of the fly ash particles, (b) their fineness and (c) their chemical composition. In addition, since the type and the amount of glass present in the fly ash significantly affect its reactivity, this property was also included in the investigation. Twenty different fly ashes (both, ASTM Class C and Class F), obtained from power plants in and around Indiana, were characterized during the Phase 1 of the study. The information collected included: physical characteristics, chemical composition and the amount and type of glass present. Phase 2 of the study consisted of evaluation of various properties of binary paste systems (portland cement with 20% of cement of fly replacement). The evaluated properties included: the set time, the heat of hydration, the strength activity index, the non-evaporable water content and the amount of calcium hydroxide formed at different ages. These results obtained from both phases of the study were used to build statistical models for prediction of previously evaluated properties for any hypothetical fly ash with similar characteristics. The models included only the most significant variables, i.e., those which were found to most strongly affect any specific property. The variables to be included in the model were selected based on the adjusted R2 values. As a result of the modeling process, it was found that the sets of statistically significant variables affecting the properties consisted of both physical and chemical characteristics of the fly ash and that the combination of these variables was unique for each property evaluated. When applied to a set of results from two additional (not previously used) fly ashes, the models provided the following residuals of predicted properties: (a) Initial set time – 100 minutes for Class F ashes and over 300 minutes for Class C ashes (b) Peak heat of hydration – 0.7 W/kg (c) Time of peak heat – 375 minutes (d) Total heat of hydration – 96 J/kg (e) Calcium hydroxide content at various ages – 0.25% for early ages (1 and 3 days) and 0.5% for later ages (7 and 28 days) (f) Non-evaporable water content – 0.7% for early ages (1 and 3 days) and 5% for later ages (28 days) (g) Strength activity index – range of 1% in Class C ashes and 1% to 2% in Class F ashes (from 7 days to 28 days) Phase 3 of the study consisted of evaluating the same set of properties but using ternary paste systems (cement and two different fly ashes). The goal for this study was to ascertain the applicability of the weighted sum of the models chosen for the binary paste systems to predict the properties of ternary binder systems. In addition, the analysis as to which of the chosen variables has the maximum effect on the properties was performed. It was found that the properties of the ternary binder systems were not additive in nature, except for strength activity index at 28 days. Lastly, the percent influence of each of the chosen independent variables, which affect the mentioned properties, was calculated along with the unexplained variation (error percentage). The error percentages varied for each of the properties, with set time having the maximum error (almost 50%)

Compatibility of Cementitious Materials and Admixtures

Growing demand for creating more sustainable and durable concretes lead to the increased usage of various cementitious materials and chemical admixtures in the mixtures. However, the increased usage of these components resulted in more complex mixtures that sometimes cause unexpected incompatibility problems. This report summarizes the results of the investigation of the parameters that may lead to workability problems, early age hydration irregularities and difficulties in achieving quality air void system in both plain and fly ash cementitious mixtures. The present research work was performed in three major phases and the statistical modeling was used to aid in interpretation. Phase I involved evaluation of more than 100 different paste and mortar mixtures with respect to potential slump loss and hydration irregularities. The results showed that cements with high C3A and low SO3 content were more prone to incompatibility problems. It was also observed that mixes with lignin based water reducing agent (WRA) had higher tendency for rapid stiffening than mixes with polycarboxylate type superplasticizer (PCSP). Increased replacement of cement by class C ashes resulted in the development of abnormal secondary peaks in semi-adiabatic calorimetry curves and accelerated the setting behavior. The focus of phase II was on identifying material combinations that can result in problems related to air void generation and stability. The experiments were conducted on 18 different systems and included determination of foam drainage and foam index parameters. The results show that the amount of air entrainers required to obtain target air percentage, increased with the increase in the fly ash content in the mixture. Lignin based WRA had, in general, a higher air entraining effect than the super-plasticizer when used in combination with air entrainers. Also, five out of the six mixtures with most unstable air void system, identified using the foam drainage experiments, contained the PCSP. The third (and final) phase of the study involved production of 10 concrete mixtures to verify the incompatibility findings from the paste and mortar experiments performed in phases I and II. The observations from the concrete testing were in agreement with the findings from the paste and mortar testing. Statistical modeling (performed using the material properties and results from phase I) identified the total C3A, SO3 and Na2Oequ contents of the binder system along with dosage of PCSP (if present in the mixture) as statistically significant in predicting the initial set time and area of spread (measured using the mini-slump test)

Development of Subgrade Stabilization and Slab Undersealing Solutions for PCC Pavements Restoration and Repairs

The loss of functionality and the development of distress in concrete pavements is often attributable to the poor subbase and subgrade conditions and/or loss of support due to the development of the voids underneath the slab. Subgrade soil stabilization can be used as an effective approach to restore the functionality of the subgrades in patching projects. This research had two main objectives: (1) identifying the best practices for soil stabilization of the existing subgrade during pavement patching operations and (2) identifying and developing new, modified grouting materials for slab stabilization and undersealing. Various stabilization scenarios were tested and showed improved performance of the subgrade layer. The use of geotextile along with aggregate course was found to significantly reduce the settlement. Non-removable flowable fill was also found to significantly reduce the subgrade settlement. Cement-treated aggregate and lean concrete provided the best performance, as they prevented formation of any noticeable settlement in the underlying subgrade

Using Modified Mortar-Bar Test Method to Access the Effects of Deicers on Expansion of Mortars With and Without Reactive Aggregates

The influence of deicing chemicals on alkali reactivity of aggregates is still an area of active research. The potential alkali reactivity of aggregates is often tested using the ASTM C1260 method. This research used the modified ASTM C1260 to test the potential alkali reactivity of aggregates. The modification included replacing the standard 1N sodium hydroxide (NaOH) used in ASTM C1260 with eutectic concentrations of the three common chloridebased deicing chemicals: sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2). The results showed that the mortar bars with reactive aggregate (Jobe sand) stored in NaCl solution developed higher expansion than those stored in MgCl2 and CaCl2 solutions. It seems NaCl can initiate (or accelerate) the alkali silica reaction (ASR), while MgCl2 and CaCl2 do not seem to contribute to ASR. In addition, after about 100–120 days of exposure, irrespective of whether they contained reactive (Jobe sand) or nonreactive (Ottawa sand) aggregates, the mortar bars submerged in the MgCl2 solution started to crack and disintegrate. This implies that the observed expansions should be attributed solely to the effect of these deicers on the cement paste itself rather than to their effects on aggregates. The proposed modified test method produced conclusive results within a relatively short testing time (~28 days)

Investigation of Premature Distress Around Joints in PCC Pavements: Parts I & II

Some of the Indiana concrete pavements constructed within the last 10-20 years have shown signs of premature deterioration, especially in the areas adjacent to the longitudinal and transverse joints. This deterioration typically manifested itself as cracking and spalling of concrete combined with the loss of material in the direct vicinity of the joint. In addition, in some cases “bulb-shaped” damage zones were also observed under the sealed parts of the joints. The objective of this study was to investigate possible causes of this premature deterioration. To reach this objective, the characteristics of the concrete in and near the deteriorated joints were compared and contrasted to the concrete characteristics in the non-deteriorated sections of pavement. The study was conducted in two different phases (Phase I and Phase II), and the findings are presented as a two-part report. The investigation started with a detailed inventory of selected areas of affected pavements in order to identify and classify the existing types of distresses and select locations for collection of the cores. During the Phase I of the study a total of 36 concrete cores were extracted from 5 different pavements.. During Phase II of the study a total of 18 cores were retrieved from five different pavement sections and subject to examination. The cores were subjected to eighth different tests: air-void system determination, Scanning Electronic Microscopy (SEM) analysis, X-ray diffraction (XRD) analysis, sorptivity test, freeze-thaw & resonance frequency test, resistance to chloride ion penetration (RCP) test and chloride profile (concentration) determination. The test results identified several cases of in-filling of the air voids (especially smaller air bubbles) with secondary deposits. These deposits were most likely the result of the repetitive saturation of air voids with water and substantially reduced the effectiveness of the air voids system with respect to providing an adequate level of freeze-thaw protection. Specifically, it was observed that the existing air void system in the concrete from panels near the deteriorated longitudinal joint had neither spacing factors nor specific surface values within the range recommended for freeze-thaw durability. Contrary to this, nearly all the concrete in lanes without damage had an adequate air void system at the time of sampling. In addition, the affected concrete often displayed an extensive network of microcracks, had higher rates of absorption and reduced ability to resist chloride ions penetration. From the observation of the drains performed using the remote camera it was obvious that not all the drains were functioning properly and some were entirely blocked. However, more precise or direct correlations could not be made between the conditions of the drains and observed pavement performance

Joint Deterioration in Concrete Pavements

Concrete pavements located in cold climates have been experiencing premature joint deterioration. Entrapment of moisture in the joints saturates the surrounding concrete, rendering it susceptible to freeze-thaw damage. To identify and to isolate the variables that might be causing this localized deterioration, concrete cores were obtained from deteriorated and non-deteriorated sections of US 35, SR 38 and SR 3 located near Indianapolis, Indiana and I-94 (located near Michigan City, Indiana). The visual evaluation of the condition of the pavement revealed that the drainage of the joints contributes significantly to their performance. Specifically, all deteriorated joint core holes drained poorly when compared to well performing joint core holes or mid panel joint core holes. Hardened air void parameters were determined following the procedure described in ASTM C457 and results for cores from deteriorated and non-deteriorated regions of the pavements were compared. The chemical and microstructural changes occurring in concrete were investigated using scanning electron microscope. Concrete panels with poor values of spacing factor and specific surface area were more prone to premature joint deterioration. Visual observation of coring sites on I-94 showed that unsealed joints performed better than sealed joints

Field Trials of Rapid-Setting Repair Materials

The primary objective of the present study was to identify the critical properties (based on the laboratory tests) that could be correlated to the field performance of the rapid setting repair materials. The first phase of the project involved laboratory evaluation of six commercial rapid-setting repair materials (RMs). When tested in the laboratory, all but two exhibited acceptable rates of strength gain and three RMs displayed relatively poor freeze-thaw resistance. All the RMs exhibited acceptable values for free-shrinkage, high resistance to cracking and good bond to substrate concrete. The resistance to chloride ion penetration of one of the RMs was very poor. The second phase of the project involved field installation and performance evaluation of the RMs. It was seen that while, in most cases, the controlled laboratory conditions yielded consistent mixes and acceptable performance, the properties of mixes produced on site were more variable. This variability was the result of somewhat uncontrolled changes in the amount of aggregate extension used, moisture content of the aggregates, amount water added and ambient temperature conditions. Follow-up inspection of the repair patches indicated that all the patches except one underwent premature failures (primarily cracking and edge de-bonding). The ambient temperature during the repairs was around 10°C and this led to an extended set-time for all the materials. The 12-hr compressive strengths values of the specimens from the field-mixes were in some cases lower than the 4-hr compressive strength values of laboratory mixes. Since the repairs were open to traffic after approximately 4 hours after placement, the low early age strengths could be a potential reason for premature failures of some of the patches. In general, several materials were found to be very sensitive to excess water added during mixing resulted in a significant impact on the durability properties – especially the freeze-thaw resistance. In the field, for most of the materials, the consistency of the mixes varied from batch to batch – this can be attributed to the variations in the aggregate extension adopted, mix-water added and also the moisture content of the aggregates used. Construction related issues (consolidation and finishing) also played an important role in the performance of the repair patches. Based upon laboratory and field results, modifications to the current INDOT performance specifications for rapid-setting repair materials have been suggested. Some recommendations for improvements in quality control measures of field-mixes and construction related issues have been suggested. Future research directions involving the evaluation of the robustness of the repair materials with respect to the uncertainties present on site have also been highlighted