Portland Cement Concrete Materials Research Articles

Adhesion characterisation of Portland cement concrete and alkali-activated binders

Alkali-activated binders (AABs) are investigated for their potential use as repair materials of Portland cement concrete (PCC). The adhesion characterisation of PCC and repair materials using AAB made from fly ash (FA) and Portland cement (PC) activated with sodium hydroxide and sodium silicate solutions, AAB made from FA and calcium hydroxide (CH) activated with sodium hydroxide and sodium silicate solutions, and commercial repair materials (RMs) have been investigated. Test results show that the AAB with additives gives high bond strength which is similar to the use of RMs. Bond strength between PCC substrate and AAB with additives is improved, due to increased reaction products, especially calcium–silicate–hydrate gel. However, the CH replacement at 15% shows a large amount of calcite resulting in a reduction in bond strength. The failure patterns and fracture interface images of the tested specimens also demonstrate the quality of the developed bond strength. It is shown that the interface zone of PCC substrate and AAB is homogeneous with no visible gap between the two bonding surfaces. It is suggested that the AAB with PC as additive can be used as a repair binding material which not only has high bond strength but is also cost-effective.

Modeling in Situ Performance of Cement-Stabilized Granular Base Layers of Urban Roads

This study used a three-dimensional nonlinear orthotropic computational road model to measure the performance of reclaimed and recycled portland cement concrete (PCC) aggregates and reclaimed asphalt pavement (RAP) aggregates stabilized with cement as a base layer in a typical local road structure in the city of Saskatoon, Saskatchewan, Canada. The pavement structure was composed of 45-mm hot-mix asphalt concrete on a 225-mm granular base built directly over an in situ subgrade. The cross section was analyzed with a conventional granular base layer as a baseline and PCC and RAP base layers with 2% cement stabilization. The cement-stabilized PCC and RAP base layers showed improved shear strain and horizontal strain behavior when compared with the conventional granular base layer (which was not cement stabilized). This improvement con-firmed that cement stabilization of reclaimed PCC and RAP materials provided an enhanced primary response. This study demonstrated that typical thin Saskatoon pavement structures were highly dependent on the constitutive properties of base layer material. Stabilizing the PCC and RAP base layers with 2% cement reduced the maximum shear strains at the edge of the pavement structure by 12% and 25%, respectively, compared with the unstabilized conventional granular base layer. It was believed that the increased fracture and cohesion of the residual cementitious materials inherent to recycled granular base, as well as the cementitious binder added, improved structural performance.

Cement Stabilization of Conventional Granular Base and Recycled Crushed Portland Cement Concrete

Challenges in finding high-quality sources of natural aggregate have led Saskatchewan, Canada, road agencies to explore alternative solutions to meet aggregate demands. The use of recycled materials, such as recycled portland cement concrete (PCC), though traditionally limited to low-quality applications such as subbase or backfill materials, shows promise as a technically viable solution that also offers economic and environmental advantages. In this study, mechanistic material testing was used to examine the effects of cement stabilization on traditional granular base and on two impact-crushed recycled PCC materials from different locations. The unstabilized PCC materials had substantially better mechanistic material properties than the unstabilized conventional granular base material; this result indicates that PCC materials could be suitable for use in high-quality applications, such as base course layers, rather than being limited to use in low-quality applications, such as utility and embankment fills. This study also showed that cement stabilization substantially improved the mechanistic properties of conventional granular base material, yet had a much less pronounced effect on the material properties of the PCC materials. This result may be attributable to poor absorption of the cement by the PCC or a lack of rehydration of the PCC. There was minimal variability in the mechanical behavior of the PCC specimens despite a difference in stockpile location. Both types of PCC material were processed and crushed with the same technique and equipment.

Performance Related Tests on Recycled Materials for Sustainable Design of Pavement Systems

Abstract This paper provides recommendations for performance-related tests to select recycled materials to be used in pavement foundations (base/sub-base layers). The test protocol presented in this paper will help transportation agencies, pavement design engineers and construction industry professionals to mechanistically evaluate and select sources of recycled hot-mix asphalt and portland cement concrete materials and identify factors that contribute most to the longevity of layers using recycled pavement materials. Extensive literature review was conducted on the aggregate specifications in the United States and other countries to identify the protocols used to evaluate the suitability of virgin and recycled aggregates in base and sub-base layers. The test procedures, typically designed for virgin aggregates, were modified to account for the recycled materials in the aggregate mix. The test procedures were further evaluated on the basis of mechanical performance, accuracy, practicality, complexity, precision, and test cost. The performance of the developed aggregate evaluation systems was determined through testing and analysis of 12 aggregates with different lithology and known field performance history. These samples were selected from seven states with different seasonal frost cycles. The performance tests were conducted and modifications were made to the tests procedures to better understand the mechanical behavior of aggregate systems with recycled materials. This study revealed that shear strength, toughness, abrasion, durability, and frost susceptibility influence the performance of the unbound aggregate layers. Statistical analysis of the data showed that shear strength of the aggregate systems has the most impact on the performance of the unbound systems consisted of recycled materials.

Mechanistic Design and Nondestructive Structural Validation of a “Green Street” Test Section Using Recycled Rubble Materials

The City of Saskatoon, Saskatchewan, Canada, commissioned the “Green Street” Infrastructure Program to investigate the potential of using recycled reclaimed asphalt pavement (RAP) and portland cement concrete (PCC) rubble as structural road layers. This study validated the mechanistic materials characterization and structural design of a field test section constructed using recycled RAP and PCC materials in addition to in situ reclaimed and recycled road materials. This paper presents a summary case study of the Green Street test section on 8th Street in Saskatoon. The rehabilitation of 8th Street consisted of two pavement rehabilitation systems: one incorporated a drainage layer and the other did not. The rehabilitation of the right-turn lane included a drainage system incorporating City of Saskatoon offsite impact-crushed PCC rubble material. The entire right-hand-turn lane and sections of the median lane and the driving lane were rehabilitated by rotomixing hot-mix asphalt concrete (HMAC) and granular base layers and adding offsite impact-crushed RAP to top up the remixed base layer. The top 200 mm of this remixed base layer was stabilized with cement–emulsion. The entire 8th Street test section was surfaced with typical City of Saskatoon HMAC. When subjected to mechanistic triaxial frequency sweep characterization, both the cement–emulsion-stabilized in situ remix material (utilized as a black base course) and the HMAC surfacing materials showed good mechanistic structural material constitutive behavior. The stabilized in situ remix material yielded end-product mechanistic material behavior that exceeded that of the HMAC surfacing.

Evaluation of Characterization and Performance Modeling of Cementitiously Stabilized Layers in the Mechanistic–Empirical Pavement Design Guide

Cementitious stabilization of aggregates and soils is an effective technique to increase the stiffness of base and subbase layers. Furthermore, cementitious bases can improve the fatigue behavior of asphalt surface layers and subgrade rutting over the short and long term. However, it can lead to additional distresses such as shrinkage and fatigue in the stabilized layers. Extensive research has tested these materials experimentally and characterized them; however, very little of this research attempts to correlate the mechanical properties of the stabilized layers with their performance. The Mechanistic–Empirical Pavement Design Guide (MEPDG) provides a promising theoretical framework for the modeling of pavements containing cementitiously stabilized materials (CSMs). However, significant improvements are needed to bring the modeling of semirigid pavements in MEPDG to the same level as that of flexible and rigid pavements. Furthermore, the MEPDG does not model CSMs in a manner similar to those for hot-mix asphalt or portland cement concrete materials. As a result, performance gains from stabilized layers are difficult to assess using the MEPDG. The current characterization of CSMs was evaluated and issues with CSM modeling and characterization in the MEPDG were discussed. Addressing these issues will help designers quantify the benefits of stabilization for pavement service life.

Mechanistic Laboratory Evaluation and Field Construction of Recycled Concrete Materials for Use in Road Substructures

Given the renewal of urban infrastructure and the increased costs of landfilling concrete rubble materials, opportunities exist to optimize the reclamation and recycling of portland cement concrete (PCC) and hot-mix asphalt concrete (HMAC) rubble through their innovative use in road rehabilitation. The primary objective of this study was to demonstrate the ability to reclaim, process, and recycle stockpiled concrete materials to provide improved structural mechanistic–climatic material properties and to meet or exceed the mechanical properties of conventional granular road materials. This research was based on advancements made in 2009 as part of the Green Streets Infrastructure Program in the city of Saskatoon, Saskatchewan, Canada. A second objective of this research was to pilot the field application of reclaimed and recycled HMAC and PCC rubble in typical urban road reconstruction applications. Recycled HMAC and PCC materials were used in the pilot reconstruction of a road that was exhibiting substructure moisture problems and structural failure. This study showed that recycled HMAC and PCC rubble materials could be processed to achieve mechanistic laboratory properties that exceeded those of conventional granular-based materials. This study also demonstrated efficient constructability and high end-product structural asset value of a typical rehabilitated urban road structure test section in the city of Saskatoon by using recycled HMAC and PCC rubble. On the basis on these findings, the use of quality processed HMAC and PCC rubble materials for road reconstruction was found to be a technical and environmentally sustainable solution.

Estimating the Sensitivity of Design Input Variables for Rigid Pavement Analysis with a Mechanistic–Empirical Design Guide

Many highway agencies use AASHTO methods for the design of pavement structures. Current AASHTO methods are based on empirical relationships between traffic loading, materials, and pavement performance developed from the AASHO Road Test (1958–1961). The applicability of these methods to modern-day conditions has been questioned; in addition, the lack of realistic inputs regarding environmental and other factors in pavement design has caused concern. Research sponsored by the NCHRP has resulted in the development of a mechanistic–empirical design guide (M-E design guide) for pavement structural analysis. The new M-E design guide requires more than 100 inputs to model traffic, environmental, material, and pavement performance to provide estimates of pavement distress over the design life of the pavement. Many designers may lack specific knowledge of the data required. A study was performed to assess the relative sensitivity of the models used in the M-E design guide to inputs relating to portland cement concrete materials in the analysis of jointed plain concrete pavements. Twenty-nine inputs were evaluated by analysis of a standard pavement section and change of the value of each input individually. The three pavement distress models (cracking, faulting, and roughness) were not sensitive to 17 of the 29 inputs. All three models were sensitive to six of the 29 inputs. Combinations of only one or two of the distress models were sensitive to six of the 29 inputs. These data may aid designers in focusing on inputs that have the most effect on desired pavement performance.