Performance Evaluation of Strengthening Recycled Coarse Aggregate in Cement Stabilized Mixture Base Layer of Pavement

This paper attempts to study the effect of different strengthening methods on recycled coarse aggregate (RCA) reprocessed from construction and demolition (C&D) waste. And it aims to obtain the optimal RCA content in cement stabilized recycled mixture (CSRM) applied in the base layer of pavement. Firstly, three strengthening methods were used to strengthen the RCA. It was revealed that the sodium silicate solution is the best method in a strengthening concentration of 8% and strengthening for five hours. Then, the mechanical experiments under two cement dosages, including unconfined compressive strength, splitting strength, and compressive rebound modulus tests, were carried out. In each cement dosage, five different RCA contents (0%, 25%, 50%, 75%, and 100%) were considered. It was found that, at 5% of cement dosage, the strength of CSRM satisfied the requirements of the base layer of the expressway under heavy traffic load. In the case of 4% of cement dosage, the strength of CSRM which was beyond 50% of RCA content was failed to meet specification requirements. For the failed cases, by strengthening RCA in the best method obtained before, 7 d unconfined strength and crushing value of the CSRM with 50% RCA content could meet the requirements of the subbase of expressways and first-class highways in China; the 75% of the mixture meets the requirements of the second-class highways and below.

Nondestructive Testing of Stabilized Soils and Soft Rocks via Needle Penetration

Assessing the strength of hard soils and soft rocks is a pressing issue in geotechnical investigations, since high quality core samples recommended by testing standards for strength determinations cannot always be achieved. As a solution, a light-weight, non-destructive testing device, Needle Penetrometer (NP), was developed in Japan. It is not well known and standardized in other parts of the world. No sample preparation is required, and it is applicable both in the field and laboratory with minimum surface conditioning. This study aims to provide some new contributions to previous works on the NP test, including new rock types and stabilized soils. For these purposes, unconfined strength (UCS) and needle penetration resistance (NPR) values were determined for compacted clays, lime and cement stabilized clays, micritic tufa, microdetrital tufa and pumice. A database consisting of a total of 108 UCS–NPR data pairs was established. Regression analyses reveal that, there is a significant relationship between UCS and NPR. It is concluded that the NP tests can be applied to stabilized soils and soft rocks with UCS of up to 30 MPa to predict the UCS from NPR.

Feasibility of Pulverized Oyster Shell as a Cementing Material

This research intends to study the cementing potential of pulverized oyster shell, rich in calcium, when mixed with fly ash and soil. Cylindrical compacted soil and cubic lime specimens with different proportions of the shells and fly ash are made to study the strength variance. Soil, which is classified as CL in the USCS system, commercialized pulverized oyster shell, F-type fly ash, and lime are mixed in different weight percentages. Five sample groups are made to study the compressive strength of soil and lime specimens, respectively. The lime cubes are made with 0.45 W/B ratio and the cylindrical soils are compacted under the standard Procter compaction process with 20% moisture content. The results show that increment of shell quantity result to lower strength on both the soil and lime specimens. In a 56-day curing, the compressive strength of the lime cubes containing fly ash increases evidently while those carrying the shell get little progress in strength. The soil specimens containing fly ash gradually gain strength as curing proceeds. It suggests that mixtures of the shell and fly ash do not process any Pozzolanic reaction nor help to raise the unconfined strength of the compacted soil through the curing.

The Choice of Basic Pillar Design Theory for Locked Sand Condition

Because of unique properties of locked sand (very high friction angle and very low cohesion), a new pillar design method based on present basic pillar design theories must be developed. Wilson theory puts its focus on confining pressure, which is related to friction angle and cohesion. Triaxial tests results show that locked sand at Pattison mine has an average friction angle of 57°, which means the strength of the material increases rapidly with the confining pressure, and average cohesion of 2.6 MPa. Results show that choosing Wilson theory as basic pillar design theory not only considers the high friction angle of locked sand, but also minimizes the effects of Wilson’s hypothesis of neglecting the unconfined strength.

Experimental Study of the Impact of PAM on Cement Soil Strength

This paper studys the effect of PAM on the strength of cement-soil by different PAM content cement soil unconfined strength test combined with a scanning electron microscope test to have a microscopic analysis of the impact mechanism of PAM on the strength of cement-soil, hoping to cement soil engineering applications to provide a reference. The study shows that: when cement content is 10%, the compressive strength trend of cement soil is first rose and then decreased with the increase of PAM content . Cement-soil that was mixed with an appropriate amount of PAM can effectively improve the compressive strength of cement-soil and there is an optimal content.

Development of a New Reclamation Material by Hazardous Waste Solidification/Stabilization

This paper deals with the possibility of hazardous waste solidification/stabilization (S/S) using a secondary raw material – fly ash from fluidized bed combustion – in order to find and verify a suitable S/S formula and an appropriate way to ensure that the properties of the S/S product will allow its further use in civil engineering as a reclamation material. The aim of this paper is to examine the properties of the S/S product and to assess its impact on the environment. Laboratory testing was focused on screening those properties that may adversely affect the environment during the use of the product on the ground surface. During laboratory testing the S/S product’s properties were verified using leaching tests, unconfined strength testing, ecotoxicological tests and the determination of pollutant content in dry matter. This paper also considers the two-year durability of the S/S product’s properties in order to verify the short-term durability of the S/S matrix.

Study on Solidification Mechanism of Chloride Salt in Base Course Material of Cement-Fly-ash-Flushed-by-Seawater

Through analyzing the influence of different slat content on the microstructure of cement and fly-ash-flushed-by-seawater binder, the solidification mechanism of salt added cement and fly-ash-flushed-by-seawater binder is investigated. The Scanning Electron Microscope test, X-Ray diffraction and theoretical analysis method are adopted to study the performance and the microstructure of cement and fly-ash-flushed-by-seawater, and to analyze the solidification mechanism of chloride in the mixture. When content of the chloride ions is added to the cement and fly-ash-flushed-by-seawater binder, a new kind of crystal-Friedel can be generated in the age of 7d and 28d. According to the unconfined strength test on the specimens which contain 0.5% chloride ions, the strength is high in 7d, highest in 28d. The chloride ions of the fly-ash-flushed-by-seawater can be solidified in the cement and fly-ash-flushed-by-seawater binder, which can increase the strength of the binder.