Monica Prezzi

Chemical, Mineralogical, and Morphological Properties of Steel Slag

Steel slag is a byproduct of the steelmaking and steel refining processes. This paper provides an overview of the different types of steel slag that are generated from basic-oxygen-furnace (BOF) steelmaking, electric-arc-furnace (EAF) steelmaking, and ladlefurnace steel refining processes. The mineralogical and morphological properties of BOF and electric-arc-furnace-ladle [EAF(L)] slag samples generated from two steel plants in Indiana were determined through X-Ray Diffraction (XRD) analyses and Scanning Electron Microscopy (SEM) studies. The XRD patterns of both BOF and EAF(L) slag samples were very complex, with several overlapping peaks resulting from the many minerals present in these samples. The XRD analyses indicated the presence of free MgO and CaO in both the BOF and EAF(L) slag samples. SEM micrographs showed that the majority of the sand-size steel slag particles had subangular to angular shapes. Very rough surface textures with distinct crystal structures were observed on the sandsize particles of BOF and EAF(L) slag samples under SEM. The characteristics of the steel slag samples considered in this study are discussed in the context of a detailed review of steel slag properties.

A New Slurry-Based Method of Preparation of Specimens of Sand Containing Fines

A new method of specimen reconstitution is presented that is appropriate for element testing of sands containing either plastic or nonplastic fines. The method allows reconstitution of homogeneous, saturated specimens of sands containing fines whose stress-strain response closely resembles the stress-strain response of natural soil deposits formed underwater (e.g., alluvial and offshore submarine deposits, hydraulic fills, and tailings dams). A procedure is described to evaluate the maximum void ratio (emax) of sands containing fines under conditions that more appropriately represent soil deposition at its loosest state in aquatic environments. For soils deposited in water, the data obtained with the procedure proposed in this paper suggest that ASTM D 4254 overestimates the emax of sands containing plastic fines and underestimates the emax of sands containing nonplastic fines.

The alkali-silica reaction, part I: Use of the double-layer theory to explain the behavior of reaction-product gels

An understanding of the expansion mechanisms resulting from alkali-silica reaction is necessary to assess the susceptibility of a concrete structure to deterioration by these processes and to the planning and implementation of preventive measures. As a result of the alkali-silica reaction between certain reactive aggregates and the highly alkaline pore fluids in a cement paste, a reaction-product gel develops that, in the presence of water, expands and may cause cracking of mortar or concrete. To explain the volume change behavior of mortar bars containing a reactive aggregate, a theoretical model is proposed in this paper. The expansion of the alkali-silica reaction-product gels is attributed to swelling caused by electrical double-layer repulsive forces. For a given colloidal system, double-layer theory indicates that the larger the valence of the counterions in the double layer, or the larger the concentration of these ions, the smaller the double-layer thickness and the repulsive forces that may be generated in the presence of water. Results of experiments from the literature support the double-layer model. According to these results, the expansion of mortar bars in the American Society for Testing and Materials (ASTM) C 1260 test is related to the composition of the reaction product gels. The reaction-product gels containing larger amounts of equivalent sodium oxide (Na2Oe) and smaller CaO/Na2Oe cause larger expansions in the mortar bars.

ALKALI-SILICA REACTION--PART 2: THE EFFECT OF CHEMICAL ADMIXTURES

Many aggregates are susceptible to the alkali-silica reaction. As a result of this reaction, mortar bars and concrete elements containing portland cement expand. In order to limit this expansion, chemical admixtures that interfere with the alkali-silica reaction can be introduced into the mixing water. The research discussed below describes how several of these chemical admixtures affect mortar-bar expansion. Mortar bars containing any of several chemical admixtures in the mixing water at initial molar concentrations of 1 or 2 were subjected to ASTM C 1260 tests. After the expansion test, samples were prepared from each of the mortar bars and examined in a scanning electron microscope with EDX capabilities. The following chloride salts and hydroxides were used: NaOH, KOH, LiOH, NaCl, KCl, LiCl, CaCl2, MgCl2, and AlCl3. For a given initial molar concentration, the expansion test results indicated that the chloride salts with monovalent cations were the most damaging, followed by those with divalent and trivalent cations. These results are in agreement with a theoretical model presented in a previous paper that explains the volume change behavior of the reaction product gels. This model attributes the swelling of the reaction product gel to double-layer repulsion forces.

Assessment of the Axial Load Response of an H Pile Driven in Multilayered Soil

Most of the current design methods for driven piles were developed for closed-ended pipe piles driven in either pure clay or clean sand. These methods are sometimes used for H piles as well, even though the axial load response of H piles is different from that of pipe piles. Furthermore, in reality, soil profiles often consist of multiple layers of soils that may contain sand, clay, silt or a mixture of these three particle sizes. Therefore, accurate prediction of the ultimate bearing capacity of H piles driven in a mixed soil is very challenging. In addition, although results of well documented load tests on pipe piles are available, the literature contains limited information on the design of H piles. Most of the current design methods for driven piles do not provide specific recommendations for H piles. In order to evaluate the static load response of an H pile, fully instrumented axial load tests were performed on an H pile (HP 310 × 110) driven into a multilayered soil profile consisting of soils composed of various amounts of clay, silt and sand. The base of the H pile was embedded in a very dense nonplastic silt layer overlying a clay layer. This paper presents the results of the laboratory tests performed to characterize the soil profile and of the pile load tests. It also compares the measured pile resistances with those predicted with soil property- and in situ test-based methods.

Analytical solutions for consolidation aided by vertical drains

Soil disturbance caused during the installation of vertical drains reduces the in situ hydraulic conductivity of soft deposits in the immediate vicinity of the drains, resulting in a slower rate of consolidation than would be expected in the absence of disturbance. Experimental investigations have revealed the existence of two distinct zones, a smear zone and a transition zone, within the disturbed zone around the vertical drain. The degree of change in the hydraulic conductivity in the smear and transition zones is difficult to assess without performing of laboratory tests. Based on the available literature, four different profiles of hydraulic conductivity versus distance from the vertical drain were identified. Closed-form solutions for the rate of consolidation for each of these four hydraulic conductivity profiles were developed. It is found that different variations of the hydraulic conductivity profiles in the disturbed zone result in different rates of consolidation.

RELIABILITY APPROACH TO SERVICE LIFE PREDICTION OF CONCRETE EXPOSED TO MARINE ENVIRONMENTS

In the life of concrete structures they are subjected to external actions or agents that in time may alter them from a safe state to failure or a damage state. One of the processes that may trigger the onset of corrosion of steel embedded in concrete is the ingress of chloride ions that eventually reach the reinforcement, causing the rupture of the passive film. In this paper, a method is proposed for interpretation of immersion test results and prediction of the service life of concrete structures exposed to chloride ions. Once the chloride profiles are determined after the immersion test, a realization of the random diffusion coefficient is obtained at each point for which there is a measurement of the chloride content. These samples are used to predict the probability density function of the diffusion coefficient. A reliability analysis is subsequently performed for 10 different lightweight high-strength concrete mixes. A reinforced concrete element is considered to have failed when corrosion initiates at the reinforcement, i.e., after a certain chloride concentration threshold is reached at the reinforcement. The probability of corrosion initiation in time is computed for some of the concrete mixes examined.

Use of Steel Slag in Subgrade Applications

Steel slag is a by-product of steelmaking and refining processes. In 2006, 10-15 million metric ton of steel slag was generated in the U.S. Out of the total steel slag produced in the U.S. every year, about 50-70% is used as aggregate for road and pavement construction and approximately 15-40% is stockpiled in steel plants and eventually landfilled at slag disposal sites. Since current levels of steel slag stockpiling and landfilling are not sustainable, alternative geotechnical engineering applications for steel slag are being explored to alleviate the slag disposal problem and to help save dwindling natural resources. The main objectives of this research were to determine the geotechnical engineering properties of two types of steel slag generated from different steelmaking operations and to assess their potential use in subgrade stabilization and embankment construction. Samples of fresh and aged basic-oxygen-furnace (BOF) slag and of fresh electric-arc-furnace-ladle (EAF(L)) slag were characterized through a series of laboratory tests (specific gravity, grain-size analysis, X-ray diffraction, compaction, maximum and minimum density, large-scale direct shear, consolidated drained triaxial and swelling tests). The effects of gradation on the engineering properties of both fresh and aged steel slag samples were also investigated. Various mixtures of steel slag [BOF and EAF(L)] and Class-C fly ash were also investigated. The mixtures were prepared by adding 5 and 10% Class-C fly ash (by weight) to aged BOF slag and 5, 10 and 20% Class-C fly ash (by weight) to fresh EAF(L) slag. Unconfined compression tests were performed after various curing times to evaluate the strength gain characteristics of the mixtures. Long-term swelling tests were performed for compacted mixtures of both fresh and aged BOF slag and 10% Class-C fly ash (by weight) and for compacted mixtures of fresh EAF(L) slag and 5, 10 and 20% Class-C fly ash (by weight). The effect of adding 10% ground rubber (by weight) to fresh and aged BOF slag on the long-term swelling behavior of the mixtures was also investigated. The optimum moisture content and maximum dry unit weight of BOF slag were in the ranges of 4-8% and 19.5-21.8 kN/m3, respectively. The critical-state friction angle of fresh and aged BOF slags was in the 45.3°- 48.1° range according to large-scale direct shear test results. Based on isotropically consolidated drained triaxial test (CIDTX) results, the peak friction angles of aged BOF slag (with minus 9.5 mm gradation) samples prepared at 90% relative compaction were equal to 47.3°, 45.2° and 43.5° at effective confining stresses of 50, 110 and 200 kPa, respectively. The optimum moisture content and maximum dry unit weight of EAF(L) slag were in the ranges of 10-13% and 16.8-20.0 kN/m3, respectively. The critical-state friction angle of fresh EAF(L) slag was equal to approximately 40.6° according to large-scale direct shear tests results. Compacted mixtures of both Class-C fly ash and BOF slag and of Class-C fly ash and EAF(L) slag showed excellent strength gain properties with time. Results of the long-term swelling tests on steel slag and Class-C fly ash mixtures showed that the addition of 10% Class-C fly ash suppresses the swelling of both BOF and EAF(L) slag samples to negligible levels.

Shaft Resistance and Setup Factors for Piles Jacked in Clay

AbstractInstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay. The gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtaine...

Analytical solutions for a vertically loaded pile in multilayered soil

Explicit elastic solutions for a vertically loaded single pile embedded in multilayered soil are presented. Solutions are also provided for the case in which the pile base rests on a rigid material. Energy principles are used in the derivation of the governing differential equations. The solutions, which satisfy compatibility of displacement in the vertical and radial directions, were obtained by determining the unknown integration constants using the boundary conditions, Cramers rule, and a recurrence formula. The solutions provide the pile vertical displacement as a function of depth, the load-transfer curves, and the vertical soil displacement as a function of the radial distance from the pile axis at any depth. The use of the analysis is illustrated for a pile that was load-tested under well-documented conditions by obtaining load–transfer and load–settlement curves that are then compared with those obtained from the load test.