Journal of Materials in Civil Engineering

Environmental stress cracking (ESC) of polyethylene (PE) in structural applications can result in catastrophic failure without any visible warning. Polyethylene with excellent short-term mechanical strength can have poor long-term performance because of ESC. Because PE structures can have an expected service life of 50 years or more, the lack of understanding regarding their long-term mechanical performance is a major concern. For practical reasons, it is not possible to test PE for years before use. Currently, most mechanical tests for PE only run for a few hours. Therefore, it is important to understand the connections between short-term and long-term mechanical properties. Short-term mechanical behavior, such as creep over 8 h, is studied in conjunction with ESC for six high-density PE resins. In addition, the molecular structure influences on creep of PE are extensively investigated. Complex creep behavior is explained from the point of combined effects of molecular properties. It was found that high-density polyethylene (HDPE) resins with large creep strain usually exhibit high environmental stress cracking resistance. However, the short-term creep behavior of HDPE was affected by molecular weight, molecular weight distribution, and short-chain branching content of the material.

Warm mix asphalt (WMA) has been gaining attention in the past few years because it offers several advantages over traditional hot mix asphalt (HMA) during production and placement. The advantages include: (1) reduced energy consumption; (2) reduced emissions; (3) reduced binder aging; and (4) extended construction season in temperate climates. Moisture damage in a compacted HMA/WMA mixture can be defined as the separation of the asphalt binder from the surface of the aggregate in the presence of water. In this study, atomic force microscopy (AFM) was used to investigate the effects of water on the adhesion and cohesion forces in three asphalt binders (one HMA, two WMA) using four different cantilever tips with different materials. AFM is a microscope that can be used to makes high quality three-dimensional images for smooth and level surfaces. The asphalt binders were the HMA PG 70-22 binder; PG 70-22 mixed with a proprietary Sasol wax at 4% by weight to make a WMA binder; and PG 70-22 with a proprietary white powdered zeolite (similar to Aspha-min) at 5% by weight. The four different cantilever tip materials used in this study were: (1) ${\mathrm{SiO}}_2$ coated with a carboxylic acid functional group ($─\mathrm{COOH}$) to measure the cohesion forces between two asphalt molecules; (2) ${\mathrm{CaCO}}_3$ (representing calcite in limestone) particle cantilever tip to measure the adhesion forces between asphalt binder molecules and an aggregate molecule; (3) Ohio limestone tip to measure the adhesion forces between asphalt binder molecules and limestone; and (4) ${\mathrm{SiO}}_2$ particle tip (representing sandstone) to measure the adhesion forces between asphalt binder molecules and sand. Several researchers have used AFM to examine the surface free energy of adhesion or cohesion between various substances. In this study, AFM has been shown to be useful tool to evaluate the strength of bonding between three types of asphalt binder on four types of surfaces in the presence and absence of water. The adhesion/cohesion energy of warm binders was similar or better than the adhesion/cohesion energy of hot binder by using different cantilever tips. The performance of the Sasol wax was higher than the performance of the proprietary white powdered zeolite using certain cantilever tips which can be concluded from indirect tensile strength (ITS) results.

The absorption of solar radiant heat is the primary reason for the high temperature of asphalt pavement and the exacerbation of the urban heat island effect. In this paper, a novel unidirectional heat-transfer (UHT) asphalt pavement structure was proposed, which allows heat transfer along a fixed direction. The UHT effect was demonstrated under lamp lit indoor and sunlit outdoor environments. Compared with the control specimens, the UHT specimens were able to reduce the surface temperatures of 6.2°C (day) and 1.3°C (night), after one day’s cycle of simulating indoor heat absorption and release. The outdoor measurements showed that reductions of 3.4 and 1.2°C in the surface temperature of the UHT specimens were achieved during the day and night, respectively, when compared with the temperature of the control specimens. The calculation results also indicated that more than $466\mathrm{W}/{\mathrm{m}}^2$ of heat was introduced into the soil and less than $462\mathrm{W}/{\mathrm{m}}^2$ of heat was transferred out of the UHT specimens, which validated the self-cooling effect of the designed UHT structures. The proposed gradient thermal conductivity structure is a promising new technology to mitigate the urban heat island effect.

This paper presents the development of a probabilistic model for the cross-sectional area of corroded reinforcing steel bars (rebars), in order to assess the time-dependent reliability of corroded reinforced concrete (RC) structures. The indicator $R$, which is the ratio of the average to the minimum cross-sectional areas of corroded rebars, was adopted to quantify the longitudinal variation of the cross-sectional area. By using a three-dimensional laser scanning technique, the areas of the discrete cross-sections were evaluated along the length of a rebar at intervals of 1 mm. The statistical results showed that $R$ could be characterized by the Gumbel distribution. Both the location parameter and the scale parameter for the probability distribution of $R$ increased linearly with increases in the corrosion degree and were dependent on the element length and the diameter of the corroded rebar. The results of a time-dependent reliability analysis of corroded RC beams demonstrated that an element length of 150 mm should be chosen for reliability assessment and that larger diameter rebars should be chosen for structural design when the reduction of load bearing capacity caused by corrosion of rebars needs to be considered.

A laboratory study was undertaken to evaluate the influence of three cementitious additives on the indirect tensile and fatigue behavior of two subgrade soils. Hydrated lime (or lime), class C fly ash (CFA), and cement kiln dust (CKD) were used as additives. Cylindrical specimens were prepared, cured for 28 days, and subjected to different stress sequences in indirect tension to study the resilient modulus. Moreover, stabilized beam specimens were subjected to repeated cycles of reloading-unloading after 28 days of curing in a four-point beam fatigue apparatus for evaluating fatigue life and flexural stiffness. These properties were compared with those of the control soil specimens in order to determine the extent of enhancement. Results indicate that all three additives improved the indirect tensile and fatigue properties; however, the degree of improvement varied with the type of additive and soil. The properties evaluated under indirect tension mode projected 10 percent CKD with highest improvement after 28 days of curing, while evaluation under flexure mode showed 6 percent lime providing maximum enhancements in fatigue life. The properties evaluated in this study are expected to provide a better understanding of the performance of a stabilized subgrade layer in a mechanistic sense.

To evaluate the effects of beam specimen depth and aggregate size on the fracture energy of lightweight concrete (LWC), different beam specimens designated into 32 notations were tested under three-point bending. In each of the all-lightweight concrete and sand-lightweight concrete groups, the maximum aggregate size varied between 4 and 19 mm; the beam depth ranged from 150 to 600 mm in each ready-mixed concrete batch with the same mix proportions. Based on experimental observations and verification of prior empirical models, simple closed-form equations were proposed to generalize the influence of the concrete unit weight on the size effect for the fracture energy of concrete. Test results clearly showed that when the maximum aggregate size is larger than 8 mm, the aggregate size in LWC has an insignificant effect on fracture parameters such as the fracture energy, crack opening mouth displacement, and characteristic length due to crack propagation through the lightweight aggregate particles. The fracture energy of LWC was lower than that of normal-weight concrete, indicating that the size-dependence of the fracture energy increases with decreasing concrete unit weight. A comparison between the predicted and experimental fracture energies revealed that the reliability of existing models significantly depends on the concrete type and ligament depth of the beam specimen, whereas the proposed model generally gives better agreement with the test data; it consistently predicts the trend of the size effect, regardless of the concrete unit weight.

The aim of this work is to present a rational procedure for the composition of screed mortar with recycled sand at a construction site. Seven samples of construction and demolition waste were collected and milled in a hammer mill. The properties of the recycled sands were analyzed: water absorption, material finer than 75 μm, bulk density, fineness modulus, and presence of contaminants. Mortars were produced with different amounts of cement and by replacing the natural sand with recycled sand in the proportions of 50, 75, and 100% by mass. These mortars were characterized for tensile and compressive strength, density, and consistence. The screed mortars were applied over a concrete base and their performance was evaluated with regard to cracking, bond tensile strength, and impact resistance. Several correlations were obtained between the properties of aggregates, mortar, and screed, leading to a proposed methodology for recycling, dosage, and quality control of screed mortar prepared with recycled sand at a construction site. It is recommended for the screed mortar to have a cement consumption between 250 and $350\mathrm{kg}/{\mathrm{m}}^3$ and for the total amount of material finer than 75 μm to be lower than 28%.

This paper presents an experimental study on the long-term creep behaviour of adhesive anchors under sustained tensile loads in combination with different environmental exposures. A total of 72 pull-out test specimens with post-installed anchors were used. The test variables included the type of adhesive anchor, loading conditions (static, sustained), and the environmental exposures (room temperature, moisture, and freeze-thaw). Two sustained load levels of 32 kN and 48 kN (40% and 60% of the anchor’s yield strength) were considered. Sustained load tests lasted for a period of at least 90 days. The static pullout tests showed that specimens with epoxy adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. Under sustained load tests, the total displacements over the service life were extrapolated and compared to displacement limits at 50 years (room temperature) and 10 years (moisture and freeze/thaw) in accordance with ICC-ES AC308. Specimens with standard set epoxy adhesive showed insignificant creep displacement under room conditions and satisfied the displacement limits; however, when exposed to moisture noticeable higher creep displacements were recorded and total displacement failed to meet the limit. Specimens with both fast setting epoxy and methyl methacrylate based adhesives showed higher creep displacements and failed to meet the displacement limits under environmental exposure (moisture and freeze/thaw) versus those kept at room temperature.

Concrete bridge decks overlaid with asphalt wearing courses often witness early distresses, such as shoving, potholes, raveling, and slippage cracking resulting from poor bonds between the two layers with different modulus. Frequently used laboratory tests, including direct shear test, pull-off test, and torsional shear test, can not fully represent the critical conditions happening in the fields. In this study, a shear fatigue test under repetitive loads at an angle of 45° was developed instead. Three tack coat materials, including styrene–butadiene–styrene-modified asphalt, emulsified asphalt, and epoxy resin, were chosen as binding materials to form multilayer deck pavement specimens. Their performances were evaluated through shear fatigue test on a universal test machine. The shear stress and shear displacement of each specimen at failure were first identified, and then four levels of stress were selected to perform the shear fatigue test, based on which a fatigue prediction model was developed. To approximate the laboratory results to field load scenarios, an adjustment factor, representing the impacts of different load combinations on fatigue life, was introduced. The study showed that epoxy resin material has a remarkably superior shear fatigue performance compared with the other two, and the adjustment factor is heavily affected by the load combinations.

Currently, solidification/stabilization (S/S) is the most widely used pretreatment measure for sewage sludge prior to its disposal in landfills in China. Looking for an effective measure to increase the early strength of the solidified sludge has become a significant requirement for the sludge treatment market. In this study, the chemical and mechanical behaviors of the sludge samples treated by sulphoaluminate cement (SC) and ordinary portland cement (OPC) were investigated and compared by testing the nonevaporable water (NEW) and unconfined compressive strength (UCS) of the solidified sludge. This was followed by conducting scanning electron microscopy (SEM) analysis. From the perspective of the conversion of NEW, the retardation mechanisms of the hydrating reaction for the SC and OPC used in the sludge were also studied. The results showed that SC is an excellent cementitious additive with high early strength in S/S treatment for sewage sludge—much better than OPC, which is currently commonly used in sludge treatment. The UCS of the samples with a 10% mixing amount of SC and 1 day of curing can reach 50 kPa, which is the target strength for landfill disposal in China. The availability of water has proven to be a very important factor influencing the hydration of cementitious materials in sewage sludge but is usually neglected by existing studies.

Considerable interest has been directed in recent years toward the use of self-healing materials in concrete. The concept of microcapsule healing is based on a healing agent being encapsulated and embedded in the concrete. The objective of this study was to evaluate the effects of preparation parameters, namely, temperature, agitation rate, and pH on the shell thickness and size (diameter) of the microcapsules as well as to evaluate the self-healing mechanism in concrete through experimental testing performed in laboratory. Two healing agents were evaluated in this study, i.e., dicyclopentadiene (DCPD) and sodium silicate. Based on the results of the experimental program, it was determined that, as the pH was increased from 3.0 to 3.7, the shell thickness increased for sodium silicate, while the shell thickness reached a minimum at a pH value of 3.4 for DCPD. Sodium silicate shell thickness was almost twice the shell thickness for DCPD. The most uniform and coherent microcapsules were produced at a temperature of 55°C for both sodium silicate and DCPD. For the DCPD microcapsules and up to 49°C, the solution remained an emulsion and no encapsulation took place. An increase in agitation rate resulted in a decrease in the average diameter of the microcapsules for DCPD. On the other hand, the diameter of the microcapsules remained constant for sodium silicate microencapsulation as the agitation rate was increased from 250 to 550 rpm. Testing of concrete specimens modified with the two healing agents (DCPD and sodium silicate microcapsules) was conducted. For sodium silicate, an improvement of 11% in the modulus of elasticity of the concrete was observed after healing for the microcapsules prepared at a pH value of 3.1 and at a content of 5.0%. At other pH values, the effect of the sodium silicate microcapsules on the concrete performance was negligible. For DCPD microcapsules, the healing agent was effective in increasing the modulus of elasticity of concrete after cracking by as much as 30% for the microcapsules prepared at a pH value of 3.1 and at a content of 0.25%.

The main objective of this study was to investigate the effects of loading frequency and temperature on the moisture sensitivity of dense-graded polymer-modified asphalt mixtures using the creep curves derived from the dynamic creep tests. For this purpose, 96 Marshall specimens containing siliceous crushed stone aggregate with $85/100$ penetration bitumen, modified with 4.5% of styrene-butadiene-styrene (SBS) polymer modifier, were fabricated and tested at four different loading frequencies, four temperatures, and two moisture conditions, dry and wet, with three replicate specimens for each experimental combination. The results showed that both the variables of loading frequency and temperature had significant effects on the permanent strains of both the dry and wet asphalt mixtures. As loading frequency increased under the dry condition, permanent strain decreased, and among the four temperatures, the highest permanent strain was measured at the lowest loading frequency. On the other hand, as loading frequency increased under the wet condition, permanent strain increased too and among the four temperatures, the highest permanent strain was measured at the highest loading frequency.

This study was conducted to model the primary and the secondary regions of creep curves, derived from dynamic creep tests, for dense graded polymer modified asphalt mixtures under different moisture conditions. For this purpose, 96 Marshall specimens containing siliceous crushed stone aggregate with $85/100$ penetration bitumen, modified with 4.5% of styrene-butadiene-styrene (SBS) polymer modifier, were fabricated and tested at four different loading frequencies, four different temperatures, and two moisture conditions, dry and wet, with three replicate specimens for each experimental combination. Statistical analyses were carried out on the test results and two approaches were proposed to model the creep curves. In addition, a stepwise method was proposed by which it is possible to estimate the location of the boundary point connecting the primary to the secondary regions of the creep curves. The proposed models were compared to the previous ones, and demonstrated to be more accurate.

Geopolymers are an alternative binder to portland cement in the manufacture of mortars and concrete, as its three-dimensional aluminosilicate network imparts excellent mechanical properties. Use of geopolymers in place of ordinary portland cement is favored owing to the possible energy and carbon dioxide savings. River sand is another construction industry material that needs development of a sustainable alternate in India. Geopolymerization of fly ash amorphous silica mixtures is employed to produce fine aggregates as a possible replacement to river sand. Geopolymerization of fly ash amorphous silica mixtures in 10 M NaOH solution at 100°C for 7 days produced fine aggregates [termed fly ash geopolymer sand (FAPS)] that had comparable grain size distribution, specific gravity, and improved frictional resistance with river sand. The FAPS particles exhibited more alkaline pH (12.5) and higher total dissolved solids (TDS) concentration ($\mathrm{TDS}=747\mathrm{mg}/\mathrm{L}$) in comparison to the river sand specimen ($\mathrm{pH}=7.9$ and $\mathrm{TDS}=32.5\mathrm{mg}/\mathrm{L}$). However, when used as fine aggregate in mortar, FAPS–mortar specimens develop similar pH, lower TDS, similar compressive strength, and modulus in relation to river sand–mortar specimens. The experimental results suggest that FAPS particles have the potential to replace river sand in the manufacture of mortar and concrete.

This paper presents an iron wire trigger mechanism that will be used for a new generation of low-cost corrosion sensors that are wireless and do not require batteries or any other external power sources. The corrosion of thin sensor wires, 0.065 to 0.25 mm in diameter, were investigated in sodium chloride solutions and compared with the mass loss from steel coupons under similar conditions. The 0.125- and 0.065-mm wires were embedded in concrete and subjected to accelerated corrosion testing. These wires are suitable for use as triggers for corrosive salts. They behaved similarly to mild reinforcing steel used in concrete structures and their resistance increased significantly at predictable chloride levels. Prototype sensors, constructed using commercial radio frequency identification tags with a section of the antenna replaced by a wire trigger, were embedded in concrete. These results demonstrate the methodology to create successful radio frequency identification based sensors for the egress of corrosive agents, such as chlorides, into concrete.

This paper describes the results of an experimental study that uses radio frequency identification (RFID) technology to detect cracking in concrete elements. A RFID-based sensor is used to monitor the change in electrical resistance that occurs in conductive materials applied to the surface of the concrete. When the concrete substrate is strained, the conductive material at the surface is stretched, and its electrical resistance increases. If the concrete substrate is strained to the point where it cracks, the conductive material at the surface also cracks, causing its electrical resistance to increase by orders of magnitude. This paper describes how this increase in electrical resistance attributable to cracking can be detected wirelessly by RFID technology. To experimentally illustrate the application of this technology, an RFID-based sensor and conductive surface materials are used to detect cracking in the restrained ring test. The experimental results indicate that this technology can be easily implemented and successfully used for wireless crack detection in concrete and reinforced concrete members. The technology that is described in this paper is not limited to the laboratory environment and can be easily extended to field applications.

Durability is an important property that determines the long-term behavior of cement-based materials. Water and ions are transported in nanopores of calcium-silicate-hydrate (C-S-H) gels, the main element in cement-based material, which significantly influences the durability of cement. Because of its structural similarity, jennite, an important mineral analog of C-S-H gel, is first taken to investigate the transport behavior at a molecular level. In this paper, structural and dynamical properties of the water/ions and the jennite interface are studied by the molecular dynamics (MD) simulation method. On the (001) surface of jennite, water molecules diffusing in the channel between silicate chains demonstrate the following structural water features: large density, good orientation preference, ordered interfacial organization, and low diffusion rate. The channel water molecules have more H-bonds connected with the neighboring water molecules and solid surface. As the distance from the channel increases, the structural and dynamical behavior of water molecules varies and gradually translates into bulk water properties at 10–15 Å from the liquid-solid interface. With respect to the interaction between jennite and the ions, the surface demonstrates ${\mathrm{Cl}}^{-}$ repulsion and ${\mathrm{Na}}^{+}$ adsorption. With increased ion concentration, the jennite adsorption capability for ${\mathrm{Cl}}^{-}$ is enhanced because ${\mathrm{Na}}^{+}$ and ${\mathrm{Cl}}^{-}$ aggregate to form a cluster in the interfacial region. The simulation results, matching well with the ${}^{35}\mathrm{Cl}$ Nuclear Magnetic Resonance (NMR) studies and isotherm adsorption tests, give a molecular-scale interpretation of experimental studies.

Use of recycled asphalt shingles (RAS) into asphalt mixture has become more popular in asphalt paving industry due to dwindling natural resources and potential economic benefits. However, one critical question arises as to how much of aged asphalt binder in RAS can be effectively blended with virgin binder during mixing and construction. This paper presents a laboratory study in which gel permeation chromatography (GPC) was used to determine the blending efficiency of RAS. A correlation was first established between percentages of large molecules (LMS) obtained from GPC and rheological properties of RAS binders. Then the relationship was used to estimate the blending efficiency of RAS binders. The effects of aggregate size, RAS content, and mixing time on blending efficiency were evaluated. The test results show that the percentage of LMS was highly correlated with the complex shear modulus ($G^{*}$) of asphalt binder. Increasing mixing time led to a better blending of RAS mixture. Aggregate size did not show a significant effect on blending efficiency. In this study, partial blending was achieved and the most efficient blending occurred at approximately 5% RAS by weight.

Internal curing (IC) technology using prewetted lightweight fine aggregates (LWFAs) as additives has been proved an effective means for mitigating both autogenous shrinkage and early-age cracking under the sealed-cured conditions. However, complete elimination of autogenous shrinkage may not be necessary, as negative effects, such as the durability problems, might be induced by an excessive amount of LWFAs introduced. To better utilize internal curing technology for durable concretes, this study investigates the microstructure and the desorption properties of sintered fly ash and expanded shale LWFAs. The influences of these two types of LWFAs on autogenous shrinkage and internal RH development were experimentally evaluated in concrete with w/c of 0.3 and 0.4. The internal curing efficiency, defined as the relative volume ratio of LWFAs in paste matrix as compared to that used for completely mitigating autogenous shrinkage, is a function of particle size and spacing of LWFAs. The results show that 100% internal curing efficiency (no autogenous shrinkage at the age of 28 days) can be achieved if the ratio of the LWFA particle/paste proximity and the particle size ($2\overline{L}/〈R〉$) approach 1.1.

For concrete structures exposed to frost attack, cracks, or microcracks induced by freeze-thaw cycling can format interconnecting flow paths and allow more water or chloride ions to penetrate into the bulk concrete. It will subsequently facilitate further deterioration of concrete structures and accelerate the corrosion of embedded reinforced steel bars. Moreover, in reality most concrete structures are rarely fully saturated, so that chloride transportation in unsaturated concrete must be studied with respect to the water moving process in order to cover the real existing service conditions. In the current work, a numerical simulation method based on the mesoscale composite structure of concrete, named the lattice network model, is established to analyze the penetration property of concrete; especially the effects of microcracking induced by freeze-thaw damage on the unsaturated flow behavior are investigated. In the mesoscale model, concrete is treated as a three-phase composite material consisting of coarse aggregates, mortar matrix, and interfacial transition zone (ITZ) between the aggregate and the mortar matrix. The diffusivities of each phase, (i.e., water and chloride diffusion coefficients) is separately characterized and quantified in terms of the published test results. The unsaturated flow theory for capillary water absorption and chloride transport is employed to simulate the ingress of water and chloride ions into concrete. It is found that the water absorption and chloride penetration are substantially influenced by the frost action, and the cumulative absorbed water and chloride penetration depth are increased with the increase of freezing-thawing cycles (FTCs). Furthermore, the numerical predictions about water absorption and chloride profiles are compared with the experimental measurements. The comparisons indicate that numerical predictions agree very well with the test data.

A study involving two rolling-thin-film-oven–aged asphalts and their blends with 15 and 50% of extracted reclaimed asphalt pavement (RAP) binders was conducted to investigate the effect of RAP content and properties on the long-term aging characteristics of asphalt binders. The results from rheological analyses of aged, blended binders indicate that the aging characteristics of blended binders are dependent on fresh asphalt binders. The results show that the crossover frequency decreases at an exponential form as RAP concentrations increase, and the rheological index increases as RAP concentration increases. The pattern for stiffness increase as a function of aging times for RAP-blended binders is similar to that of a typical chemical-aging kinetic model, in which the stiffness increases substantially initially and then levels off at longer aging times. The results demonstrate that there is a linear relationship between the logarithm of $G^{*}$ and the phase angle for RAP-blended binders at all aging times and RAP contents, regardless of asphalt and RAP sources.

The interface shear strength properties of geogrid-reinforced construction and demolition (C&D) aggregates were determined using a modified large scale direct shear test (DST) apparatus. Comparisons were made between the results of the various C&D aggregates reinforced with biaxial and triaxial geogrids and with the unreinforced aggregates by means of the modified and conventional DST methods. The modified DST method employed sought to increase interlocking between the C&D aggregates with the geogrids and thus ascertains the true interface shear strength properties of the recycled demolition aggregates. Biaxial and triaxial geogrids were used as the geogrid-reinforcement materials. The C&D aggregates tested with the DST were recycled concrete aggregate (RCA), crushed brick (CB), and reclaimed asphalt pavement (RAP). The modified DST results indicated that the interface shear strength properties of the geogrid-reinforced C&D aggregates were higher than that of the conventional test method and the respective unreinforced materials. Geogrid-reinforced RCA was found to have the highest interface peak and residual shear strength property of the C&D materials. RAP was found to have the smallest interface shear strength properties of the C&D aggregates. The higher stiffness triaxial geogrid attained higher interface shear strength properties than that of the lower stiffness biaxial geogrid. The modified device also showed some increased measured interface coefficients compared with a conventional DST. The geogrid-reinforced recycled C&D aggregates was found to meet the peak and residual shear strength requirements for typical construction aggregates used in civil engineering applications.

Bacterially induced ${\mathrm{CaCO}}_3$ precipitation is a general phenomenon in nature. It has been proposed as an environmentally friendly strategy for the protection of cementitious materials. This paper investigates the biochemistry of ${\mathrm{CaCO}}_3$ precipitation induced by non-ureolytic bacteria of the genus Bacillus. Different calcium sources are compared for their effectiveness in bacterial mediation of precipitation. Surface treatment using this biodeposition technique is evaluated by parameters affecting the durability of cementitious materials. Outcomes from this study reveal that the type of calcium source has a profound impact on the biochemical process and the crystal form, size, and morphology of bacterially mediated mineralization of ${\mathrm{CaCO}}_3$. An organic calcium source, particularly calcium glutamate, is beneficial for efficient ${\mathrm{CaCO}}_3$ precipitation. Bacterial surface treatment on specimens results in a decrease of more than 50% in capillary water absorption and an increase of nearly 50% in resistance to carbonation; this is mainly attributed to pore blocking effects. This novel biological surface treatment shows particularly promising prospects for increasing the durability aspects of concrete constructions.

A point-loading device was used to research the breakage characteristics of single particles and to study their crushing mechanism. A series of point-loading tests were completed on the basis of cement ellipsoid particles modeled in various sizes and strengths with cement pastes. A close-packing method of equal spheres with several close-packed assemblies was generated, and the corresponding numerical models for cement ellipsoid particles were established by the discrete-element method. Experimental and numerical tests show that the high-strength materials are brittle, whereas the low-strength materials are ductile, and vice versa. A comparison of the experimental and numerical results show reasonable, rational results, and indicate that the force-displacement relationship is approximately linear for this type of granular material. A measurement-sphere method was used to trace the energy and stress distribution in the particle samples. The accumulation of dilatant deformation causes the collapse of the local skeleton structures in the cement ellipsoid particles.

This paper investigates the effect of curing environment on the strength and modal mineralogy of synthetically prepared acid sulphate soils (ASS) treated with lime and ground granulated blast furnace slag (GGBS). The treated samples were cured under various environmental conditions for up to 365 days and tested for pH, unconfined compressive strength (UCS), and changes in modal mineralogy using powder X-ray diffraction (XRD). Quantitative analysis of XRD patterns (QXRD) was carried out using the Rietveld method. Results show that a lower temperature curing environment ($<5°\mathrm{C}$) significantly retards the hydration and pozzolanic reactions, thereby inhibiting the strength development. It has been demonstrated that a GGBS content of 15 wt.%, representing a GGBS-to-lime ratio of 1.5, is optimum for a sustainable development of UCS of treated ASS cured at temperatures ranging from 19 to 22°C and humidity ranging from 45 to 100%. Higher GGBS contents ($>15\mathrm{wt}\%$) are observed to have an adverse effect on the UCS after 180 days of curing because of the formation of deleterious minerals (i.e., thaumasite).

Determination of consolidation properties of compacted lime-treated cohesive clays by the one-dimensional fixed-ring oedometer consolidation method with conventional load increment duration may not be appropriate due to immediate pozzolanic reactions, which occur in the presence of lime. An attempt has thus been made to study the effect of accelerated loading on the compressibility characteristics of two different cohesive clays originating from diversified terrains of Saudi Arabia, before and after treating them with lime. In order to study the extent of improvement on the strength characteristics upon lime treatment, a series of unconfined compression strength tests are also carried out. The effect of lime treatment on the elastic moduli has also been studied. It is observed that, prior to any treatment, the final equilibrium void ratio values increase with the increase in duration of loading for the soils. The addition of lime significantly affects the compressibility behavior of both the soils. The unconfined compressive strength and elastic moduli (initial tangent and secant moduli) values increased with an increase in lime content and curing period.