Search

Sustained casing pressure (SCP) is a common issue in the oil and gas industry. There were several solutions applied to contain it either by mechanical means or by injecting high-performing cement slurries. There are some limitations associated with these solutions such as volume loss, mechanical failures, limited expansion, exact spotting, and material deterioration with time. In this study, a novel expandable cement system contains a novel silicate aqueous alkali alumino silicate (AAAS) and zinc (Zn) metal slurry, and class G cement is introduced as an expandable solution to prevent annulus flow between the casing and formation. The silicate-based admixture reacts with the Zn metal slurry to generate hydrogen gas that results in the expansion of the cement slurry. The reaction and expansion can be controlled by optimizing the quantities of silicate systems and metal slurry. The expansive properties of the silicate system can be utilized to formulate a cement mix for plugging off the annulus flow. Cement slurries with different percentages such as 3, 5, and 8% by weight of water (BWOW) of AAAS silicate and Zn metal slurry were prepared and tested for their expansion. Several laboratory tests such as expansion, consistency, viscosity, and unconfined compressive strength were performed to assess the percentage expansion. The expansion was tested in the plastic tube as well as in expansion molds. The cement slurries were cured at 50 °C temperature in a water bath. It was observed that metal slurry upon reaction with AAAS silicate resulted in cement expansion by several percentages. The cement expansion was reduced by 16% at 8% BWOW concentration of AAAS silicate as compared to the expansion gained at 3% BWOW concentration. Further, the temperature triggers the expansion of cement slurry. The consistency and viscosity were impacted by the addition of AAAS and metal slurry. The application of expandable slurry can help in preventing the annulus flow and eliminating the safety issues associated with SCP. The expansion solution can be applied in loss circulation zones.

Reinforced concrete buildings with moment-resisting frames comprising beam–column joints (without joint shear reinforcement) designed prior to introduction of seismic codes are shear deficient when subjected to seismic loading, thereby mostly fail in shear at the core of the beam–column joint. However, those designed to the new seismic codes may fail by flexural hinging at the interface of the beam–column joint due to the yielding of the beam reinforcement at the location of highest stress demand (usually the beam–column joint interface). The shear failure has been precluded through the provision of transverse reinforcement at the joint in new design and the use of carbon fiber–reinforced polymer retrofitting in old buildings. Plastic hinge formation at the interface of the beam–column joint is critical because of its penetration into the joint and its effect on bond deterioration. In this study, eight corner-external beam–column joint specimens of 1/3 scale of a typical moment-resisting frame, made without transverse reinforcement, were tested for monotonic and reversed cyclic test under displacement-controlled regime. The control specimens failed by flexural hinging at the beam–column joint interface. The experimental results have been validated using the finite element model. The specimens were retrofitted with unidirectional carbon fiber–reinforced polymer of different layers and different length. After retrofitting, the plastic hinge was relocated to the curtailment end of the carbon fiber–reinforced polymer. The relocation of the plastic hinge resulted in higher load capacity and ductility.

This paper presents a study on the shear behavior of reinforced concrete (RC) beams strengthened by jacketing the surfaces of the beams using ultra-high performance fiber reinforced concrete (UHPC). The surfaces of the RC beams were prepared by sandblasting and UHPC was cast in situ over the surfaces of RC beams. The beams were strengthened using two different strengthening configurations; (i) two longitudinal sides strengthening (ii) three sides strengthening. The bond between normal concrete and UHPC was examined by conducting splitting tensile strength and slant shear strength tests on composite cylindrical specimens cast using normal concrete and UHPC. The control and strengthened beam specimens were tested using four-point loading arrangement maintaining different shear span-to-depth ratios. The results of tested beams showed the beneficial effects of strengthening the RC beams using UHPC, as evident from enhancement of the shear capacity and shifting of the failure mode from brittle to ductile with more stiff behavior. In addition, a non-linear finite element model (FEM) was developed to examine the sufficiency of the experimental results used to study the shear behavior of control and strengthened beams. The failure loads and the crack patterns determined experimentally matched well with those predicted using the proposed model with a reasonably good degree of accuracy.

A comparison of the thermal performance and energy efficiency of walls constructed using autoclaved aerated concrete (AAC) block with thermal insulating plaster and reflective coating and t...

Concrete water tanks have a stringent serviceability requirement in terms of limiting crack widths. Excessive cracks or cracks running across the full depth of these tanks could result in l...

Development of alkali-activated binder (AAB) is fast becoming a viable alternative to ordinary portland cement (OPC). However, key engineering properties of such a binder depend strongly on the chemical composition and fineness of the source materials in addition to the concentration of alkaline activators. In order to improve the reaction kinetics and subsequently, the mechanical strength of alkali activated concrete (AAC), nano-SiO2 was proposed as a partial replacement to natural pozzolan (NP) in this study. As the composition of alkaline activators also plays a vital role on the properties of AAC, trial mixtures were prepared with varying sodium silicate to sodium hydroxide (SS/SH) ratio. Subsequently, NP was partially replaced with nano-SiO2 in the selected mix to enhance the properties further. Fresh properties, such as, setting time of alkali-activated pastes (AAP) and the workability in terms of flow of mortar were determined. Evolution of compressive strength of concrete cured at 60 °C was monitored. Scanning electron microscopy (SEM) and X-ray diffration (XRD) were utilized to determine the morphology and mineralogy of the AAP, respectively. In addition, FTIR was used to identify functional groups formed in the AAP. The study reveals that a SS/SH ratio of 2.5 was suitable in achieving superior strength. AAC prepared using NP and nano-SiO2 exhibited improved strength and microstructural characteristics. However, 5% nano-SiO2 showed significant enhancement in the compressive strength and microstructural characteristics as compared to those prepared with other replacement levels. Consequently, the results of this study provides important information on developing NP-based sustainable building material with remarkable enhancement in the properties by adding nano-SiO2.

In this paper, the lateral response of unreinforced masonry walls (URM) subjected to different levels of axial load is studied numerically and experimentally. The walls in general are noted to exhibit increasing levels of lateral strength when the magnitude of applied compressive axial force is increased. Beyond a certain threshold magnitude of axial compression, this trend in the URM interaction diagram is then noted to be reversed in which the wall exhibits a weaker lateral response as the axial force exerted on the wall increases. An experimental program was conducted to study the lateral load response of sandstone and limestone walls. The finite element simulation using a plastic-damage model in terms of parameters that account for hardening and softening of the wall components in an ABAQUS environment was conducted, and the relationship between lateral and axial force that encompasses the entire spectrum of failure modes was established. The model was tested against available experimental data, and the interaction between lateral and axial force has been expressed in a ready to use form. The results obtained from the plastic-damage-based FEM simulation have also been compared to existing mechanistic models.

Natural pozzolan is a green and sustainable material, which has a strong potential for utilization in the geopolymer concrete. At room temperature, the development of strength in natural pozzolan based geopolymer concrete is fair, however, it is desirable, to have higher strength and to enhance the early age strength development. The effect of nano zeolite (NZ) as an additive to the mix by incorporating it at 3% and 5% by weight of natural pozzolan on the strength development and microstructural properties of natural pozzolan based geopolymer concrete mixes are presented. Scanning electron microscopy (SEM) was utilized to determine the morphology of the paste. The results indicated that 5% nanozeolite replacement resulted in superior strength and denser microstructure compared to other mixes. The addition of nanozeolite improved dissolution of source material in the alkaline activators and enhanced transformation of it to form polymeric compounds.

Sulfur storage tanks are integral parts of refineries and gas plants. During the gas sweetening process, liquid sulfur is separated in the sulfur recovery units and is stored in underground reinforced concrete tanks in liquid phase by steam-generated temperatures of 315 °F. Roof of the sulfur pit is about 300 – 400 mm thick reinforced concrete structure with two layers of reinforcement. Inside the sulfur pit, the ceiling and walls are subjected to high temperatures and highly corrosive acidic vapors above liquid sulfur line which leads to severe deterioration of concrete and corrosion of reinforcement in the roof slab. This paper presents the NDT based investigations of the roof slab of the tank using the Ground Penetrating Radar (GPR) in a typical sulfur pit with 30 years in service. GPR survey is compared with ultrasonic pulse echo and half-cell potential measurements on the slab. Compressive strength and petrographic examination of selected concrete cores and SEM/EDS and XRD tests on powder samples, from inside the pit are presented.

Concrete is an essential structural material that has long been used for the construction of buildings, bridges, tanks, pavements and variety of the other types of structures. Due to its physical properties and economical use, concrete is used extensively in the country's infrastructure. In the Oil and Gas sector, concrete infrastructures are more challenging structures, which are exposed to a highly aggressive environment. A special type of reinforced concrete structure exposed to different forms of sulfur attack is the sulfur storage structure, typically referred to as "Sulfur Pit". Sulfur Pit is an essential part of oil and gas processing facilities, where the sulfur after extraction from the hydrocarbons in Sulfur Recovery Units is stored and maintained in the liquid phase at temperatures ranging from 130 °C to 160 °C. The gas sweeting process results in the formation of acid gas consisting of H2S, water vapor in addition to residual sulfuric acid. Reinforced concrete exposed to this environment is subject to deterioration and corrosion of the reinforcing steel. This paper presents the experimental investigation of four different concrete mixes exposed to 5% sulfuric acid at ambient temperature. These mixes include normal OPC, sulfate resistant (Type V) cement, and two mixes with supplementary cementitious materials blast furnace slag (GGBFS) and Class-F fly ash. The investigation is focused on mechanical properties and mass loss of the concrete samples.

Evolution of heat due to an exothermic reaction between cementitious materials and water plays a significant role in the temperature rise in mass concrete at an early age. The temperature gradient between the core of mass concrete and its surfaces leads to the development of thermal stresses and may cause cracking if these stresses exceed the evolving tensile strength of concrete. This paper presents the results of an experimental and finite-element investigation of heat generation and dissipation in full-scale mass concrete blocks 2 m × 2 m × 2 m in size. A concrete mix with 100% OPC and 70% cement replaced by GGBFS was used in these blocks. The temperature profile across the depth of the block was measured at the centre, side and corner of the block. A semi-adiabatic calorimeter was used to measure the heat of hydration of the two concrete mixes. Finite-element simulation of these blocks captured with good accuracy the measured evolution of temperature in the blocks. Numerical simulation was subsequently used to investigate the influence of the size of the blocks, placement temperature of concrete, ambient temperature, solar radiation and type of formwork on the temperature rise and the associated potential of cracking in the mass concrete blocks.

In deeper wells, high pressure and temperature post cementing operations put extreme stresses on the cement sheath and dramatically affect the cement integrity. So, the design of the cement slurry is very important to ensure the durability and long-term integrity of the cement sheath. The design should lead to a better zonal isolation and strengthen the bonding with the casing. Furthermore, it should help to shield the casing from corroding and unpredictable shock loads in deeper zones and sustain plugs to control the lost circulation in fractured and high permeability zones. Different additives were used to provide these functions such as; polymers, fibers, and bio-medicine in concrete history. Because of their large surface areas and small size, those particles are highly being used in the petroleum industry in the latest decades. In this study, the usage of polypropylene fibers (PPF) is evaluated for oil well cement at high pressure and high temperature (HPHT) condition. The polypropylene fibers were added to the base cement in a different amount to evaluate its influence on enhancing the performance of cement. The results obtained showed that adding polypropylene fiber to the base cement has a negligible effect on cement density, rheological properties, and free water. Using polypropylene fiber (0.75% base weight of cement (BWOC)) with the base cement reduced the thickening time by 75%; from 317 minutes to 78 minutes. The addition of Polypropylene fiber (0.5% BWOC) increased the compressive strength of class G cement by 17.8%. Polypropylene fiber can be used as an alternative material for silica floor in shallow wells. Polypropylene fiber has a significant effect on reducing the porosity and the permeability of the base cement.

Nanotechnology provides a wide variety of methods to resolve industrial issues, which could not be addressed previously using customary methods. It helps enable researchers to alter properties of bulk materials at the nanometer scale. Various nanomaterials have been successfully applied in many areas of petroleum engineering, particularly in drilling fluids, lost circulation, enhanced oil recovery (EOR), and cementing. This study examines the mechanical and microstructural properties of oil well cement with nanozeolite. During this research, API Class G cement was used with various concentrations of nanozeolite. Compressive strength development of Class G cement, with and without nanozeolite, was studied using an ultrasonic cement analyzer (UCA) for 24 hours under high-pressure and high-temperature (HP/HT) conditions. The porosity and permeability of set Class G cement admixed with nanozeolite was also analyzed in an automated permeameter/porosimeter after 24 hours of curing. Microstructural examination of cement samples was performed using scanning electron microscopy (SEM). Three important parameters during well cementing operations included time to achieve 50- and 500-psi compressive strength and time to achieve 2,000-psi compressive strength. These parameters were significantly altered by adding a small percentage of nanozeolite to the neat Class G cement. The addition of nanozeolite resulted in a decrease in transition time and accelerated achievement of 2,000-psi strength. Furthermore, the porosity and permeability of the set Class G cement specimens with nanozeolite decreased substantially, thus indicating a dense microstructure of the matrix. This was confirmed by microstructural investigations using SEM. Nanozeolite is nonhazardous, nontoxic and is compatible with API Class G cement. Nanozeolite can be an effective oil well cement additive because it enhances early strength, and the final compressive strength helps improve cement durability. The accelerated compressive strength development can help decrease wait-on-cement (WOC) time, thus lowering operation costs. Additionally, denser microstructure can help restrain the invasion of corrosive formation fluids.

Cement pastes of water to cement ratio (w/c) of 0.45 with and without nanosilica are hydrated under two conditions, room condition (20 °C with 0.1 MPa pressure) and an oil well condition (80 °C with 10 MPa pressure) for 7 days. For the cement pastes with nanosilica, 1% and 3% of cements weights were replaced by nanosilica. The composition of the hardened cement pastes is investigated using X-ray diffraction (XRD). Nuclear magnetic resonance (NMR) experiments are used to quantify the silicate polymerization in hydrated cement paste. Microstructural phases are identified according to the corresponding mechanical property using nanoindentation. The results showed that under room curing conditions, hardened cement paste with 1% nanosilica has the highest level of calcium silicate hydrate (C–S–H) polymerization. However, under high temperature and pressure curing conditions, hardened cement paste with 3% nanosilica has the highest level of C–S–H polymerization. A new relatively stiff microstructural phase is observed in cement pastes incorporating nanosilica and cured under elevated pressure and temperature conditions. The significance of curing conditions and nanosilica content on the polymerization and stiffness of hydrated cement pastes are discussed.

In oil and gas well cementing, a robust cement sheath is required toensure long-term integrity of the wells. Successful completion of cementing jobhas become more complex, as drilling is being carried out in highly deviated andhigh pressure-high temperature (HPHT) wells. To gain desired compressive strength and rheological properties has become hard and complex task in HPHT wells. The use of nanomaterials inenhanced oil recovery, drilling fluid, oil well cementing and other applications isbeing investigated. Being smaller in size and having a high surface area, nanomaterials can provide solutions to challenges faced in HPHT cementing. This paper presents the results of an experimental studyconducted to investigate the effect of nanoclay as an additive, on themechanical and rheological properties of Type-G cement slurry under HPHTconditions. Nanoclay based cement mixes were prepared by replacing cementwith 1%, 2% and 3% BWOC nanoclay, and admixed with silica flour, and otherchemical admixtures. The cement slurries were prepared and cured at 290°F temperature and 3000 psi pressure condition as per API 10-B. Compressive strength and rheological properties were measured after conditioning the slurry at 194°F temperature and atmospheric pressure conditions as per API standard. It is observed that addition of nanoclay at1% BWOC in cement slurry, enhances the compressive strength as compared to base mix without nanoclay and other percentages of nanoclay (2% & 3%) BWOC. Further, it is investigated that nanoclay addition enhances the reological properties of cement slurry that could help in mud displacement depending on requirement.

To prevent cement sheath damage, a robust cement sheath is required to ensure long-term integrity and stability of the well from the imposed stresses. Successful completion of cementing job has become more complex, as drilling is being carried out in high pressure high temperature (HPHT) wells. Recently, application of nanomaterials in enhanced oil recovery, drilling fluid, oil well cementing and other applications are being explored. This paper presents the outcomes of an experimental study conducted to investigate the effect of nanoclay as an additive on the properties of Type G cement slurry under HPHT conditions. An organically modified nanoclay in which natural montmorillonite is modified with a quaternary ammonium salt is used in a cement mix, typically used in the Saudi Arabian oil field under HPHT conditions. Nanoclay based cement mixes were prepared with 1%, 2% and 3% BWOC nanoclay, along with silica flour, and other chemical admixtures. Development of compressive strength properties, microstructural studies using SEM and XRD techniques and permeability and porosity studies were conducted. It was observed that nanoclay at 1%BWOC reduced the permeability and porosity and enhanced the compressive strength with the accelerated strength development at early ages. A crystal product that is interweaved and joined together to build strong and well-proportioned structure is developed in the harden cement paste. The smaller size particles fill the capillaries of the cement paste that resulted in a dense structure of the matrix. In addition, this novel slurry formulation with low permeability and porosity and high compressive strength, is suitable in zones where the possibility of gas migration is very high.

Growing demand to drill high-pressure, high-temperature (HPHT) wells requires improved technology to overcome the HPHT challenges. Designing and testing for cost-effective cementing at simulated downhole conditions for HPHT gas and oil wells poses a challenge necessitating special consideration in the choice of cement slurry. A successful cementing job is dependent on how quickly and efficiently cement achieves its strength. Another critical aspect is to efficiently displace the mud out of the annulus by designing the cement slurry with desired rheology. Achieving desired mechanical and rheological properties of cement becomes harder and more complex at HPHT conditions. A wide variety of admixtures are commonly mixed with the oilwell cement slurries to accommodate the extensive range of pressure and temperature and achieve enhanced mechanical and rheological properties. Carbon nanotubes are one of the most recent admixture options. This paper describes a study carried out to examine compressive strength and rheological properties (plastic viscosity, yield stress and gel strength) of oilwell cement slurries integrating chemical additives and multi-walled carbon nanotubes (MWCNT) at HPHT conditions. The study determined that integrating MWCNT in oilwell cement led to substantial increase in the compressive strength values. The rheological properties of oilwell cement slurries are greatly reliant on temperature, water/cement ratio and the admixture used. The study indicated that using MWCNT in cement slurries improved the rheological properties of cement slurries and therefore their displacement efficiency in challenging conditions.

Growing demand to drill High Pressure High Temperature (HPHT) wells requires improved technology to overcome the HPHT challenges. Oil well cementing has a greater impact on the production potential of a well as compared to other operational actions. A successful cementing job is dependent on how quickly and efficiently cement achieves strength. Achieving desired mechanical properties of cement becomes harder and complex at HPHT conditions. A wide variety of admixtures are commonly mixed with the oil well cement slurries to deal with the extensive range of pressure and temperature to acquire enhanced mechanical properties depending on the combination of admixture used. Carbon Nanotubes (CNT), declared as "Miracle Material", have been one of the most recent admixtures being used to achieve the desired mechanical properties of cement slurries. This paper highlights the study carried out to examine the mechanical properties comprising compressive strength of oil well cement slurries integrating chemical additives and CNT under high pressure high temperature (HPHT) conditions. Three different percentages of functionalized multi-walled CNT's (MWCNT), at 0.1%, 0.25% and 0.5% bwoc, were mixed with Type-G oil well cement together with other additives used in HPHT applications. Compressive strength investigations (Destructive and UCA) were carried out on those slurries. SEM investigations were also conducted on selected MWCNT mixes. The study indicated that incorporation of MWCNT, at a very small percentage, in cement slurries resulted in a significant increase in the compressive strength values.

Motivated by the need to improve oil well integrity for potential carbon capture and storage through CO2 sequestration, nanosilica was hypothesized capable of improving the quality of oil well cement (OWC) in medium and deep oil wells. In this study, OWC was mixed with 1 and 3% nanosilica by weight to produce OWC pastes with water to binder ratio (w/b) of 0.45. The specimens were cured under high temperature and pressure, simulating what occurs in oil wells. A method of analysis combining Si29 nuclear magnetic resonance (NMR) and nanoindentation is proposed. The results are compared with observations extracted from nanoindentation in which classification of hydration products is based on the elastic modulus of the different categories of calcium silicate hydrate (C-S-H). The results show that the degree of hydration, the degree of reactivity, and silicate polymerization increase under the elevated curing condition compared with the ambient condition. It seems that C-S-H generated by the pozzolanic...

Experimental investigation is conducted to assess structurally the effectiveness of patch repair in axially loaded columns. Two patch repair materials are selected with high and low modulus of elasticity. The concrete columns were patch repaired under loaded and unloaded conditions. The patch repair is structurally effective for concrete columns repaired in an unloaded state. While for concrete columns repaired in a loaded state, the patch repair is structurally effective only when additional loading is applied. The load distribution between the patch repair, concrete core and steel reinforcement depends on the modulus of elasticity and areas of these components in the composite section at the repaired zone. For patch repair to be structurally effective, it is recommended to relieve the loads before the patch repair is applied either partially or totally if constructionally possible.

This paper addresses the problem of stress buildup in the repair layer of a concrete patch repair system resulting from moisture diffusion. As moisture evaporates from the repair layer into the surrounding ambience of known relative humidity, the hardened concrete substrate restrains free shrinkage movement of the repair layer. As a consequence, primary tensile stresses are set up in the repair layer together with shear and peeling stresses at the interface of the repair layer-concrete substrate. The repair layer under non-uniformly increasing tensile shrinkage stresses undergoes restrained creep in tension, which results in the development of secondary stresses in the system. The secondary stresses due to restrained creep being of opposite sign to that of restrained shrinkage serve to relieve the primary shrinkage stress field and the net or combined stress buildup as a result is reduced. A finite element based computer program used for computing the time dependent moisture loss profile in the repair system is interfaced with a finite element based 2-D stress analysis program for computing the time dependent restrained shrinkage and creep stresses. Variation of normal and shear stresses across depth and width at critical locations in the patch repair and temporal variation of these stresses are presented. Influence of ultimate free shrinkage strain e sh ∞ and the buildup of tensile stresses versus the evolution of tensile strength capacity f ′ t of the repair is highlighted. Also, possible zones of failure are identified in the repair layer and at the interface of the patch repair system.

This paper presents a finite element simulation to capture the nonlinear response of a typical low strength beam-column joint tested at ITU and also results of the finite element modeling and experimental program conducted at KFUPM for beam-column joints in reinforced concrete construction. Finite element analysis is performed using the software DIANA, simulating the concrete response through Drucker-Prager plasticity with a tension cut-off as failure criterion and using for the reinforcing steel Von-Mises plasticity with multi linear isotropic hardening. The failure mode and deformation response of low strength concrete beam-column joints was predicted with a good correlation between the experimental and finite element results.

In this paper, the seismic vulnerability of unreinforced masonry walls is assessed by conducting a numerical study on the interaction of axial and lateral resistance. The walls are modeled in an ABAQUS environment, using a plastic damage model originally developed by Lubliner et al. (Int J Solids Struct 25(3):299–326, 1989) and further extended by Lee and Fenves (J Eng Mech ASCE 124(8):892–900, 1998). The model yields interesting interactive collapse mechanisms that occur as the axial loading on the wall is increased. The different modes of failure identified as the axial load is increased include (i) rocking mode, (ii) sliding mode, (iii) staggered head/bed joint failure, (iv) diagonal cracks through wall blocks accompanied by staggered head/bed joint cracking, and (v) crushing of wall blocks or bricks.

Papers were presented by the international and regional scholars in the area of Structural Engineering. The Special Issue is a collection of the peer adjudged 18 papers from the Conference, including 4 keynote papers. Exciting new developments in the world of computational mechanics and materials are leading the way to advances in Structural Engineering. Computational modeling developments are the catalyst for a new wave of research into problems addressing nanoand micromechanical behavior, in addition to provide improved constitutive models for monotonic, cyclic and dynamic loading of structures. Innovations in materials engineering include the use of nano-technology in the production of superior concretes and adhesives, smart materials and their use in retrofitting of damaged structures, and use of new superplasticizers and mineral admixtures in the production of ultra-high strength concrete. Such developments in the world of structural mechanics and materials make demands on structural engineering researchers to match the advances, and to conceive and design structures that would take full advantage of the innovations. The use of these models and the new generation of materials by structural engineers in traditional and innovative structures are now allowing the buildings to reach higher into the skies, for bridges to traverse distances and terrain not dreamt of before and to provide for safe and stable foundations for such structures. The structural engineer has to interface with the geotechnical engineer and be cognizant of developments in geotechnical engineering. The 18 papers in the Special Issue address subjects in various broad groups, including three papers in concrete materials and durability modeling (including two keynote papers, one on nano-concrete and another on improvement of durability of post-tensioned reinforced concrete bridges), five papers in precast and prestressed concrete and bridges (including a keynote presentation on the challenge of using CFRP cables in ultra-long span suspension bridges), and two papers including a keynote address on ferrocement and fiber reinforced concrete. Considering the recent natural disasters that have occurred around the world, two papers on earthquake engineering, including a theme presentation addressing this very important topic in the regional context, have been included. Three papers on the use of FRP’s in retrofitting and repair of reinforced concrete structures, two papers on composites including a theme presentation on the design of composite columns, and one paper addressing soil–structure interaction complete the list of eighteen papers selected for inclusion. It is hoped that this Special Issue will provide researchers and practicing professionals in the Gulf region with valuable information which can be incorporated in the design of new structures and stimulate further research in structural design, constitutive modeling and computational mechanics, and concrete materials. The team of Technical Editors would like to express their deepest gratitude and appreciation first to KFUPM for hosting the 11th ASEC Conference, allowing regional and international scholars to share their experiences with the engineering community in the Kingdom. The Editors also offer thanks to the authors who responded spontaneously to the invitation to submit enhanced versions of their 11th ASEC papers for review for possible inclusion in this Special Issue. Special thanks are due to the referees for their meticulous reviews, and for their role in improving the presentations and the discussions in the papers.

Publisher Summary Durability of a patch repair has become a major concern in the recent times because of cracking and failures of repair layers over a short span of time. A phenomenological model capable of modeling a chain of critical processes that is set off in a patch repair system and results in the generation and dissipation of stresses in the system is developed. Moisture diffusion, a primary critical process in a repair system is addressed in this chapter. A non linear 2D finite element program diffusion analysis (DIANA)-2D is developed for repair systems. A phenomenological approach in which various transport mechanisms at microlevel are lumped together by defining diffusivity of the material at macroscopic level is adopted. A miniature patch repair system consisting of a thin layer of repair material placed over a hardened concrete substrate is analyzed. The spatial and temporal moisture content is obtained, and the moisture loss history over the specified time intervals is computed.

During the repair and rehabilitation of concrete structures, mistakes in design, selection of materials, and construction practices will lead to incompatibility between the repair and the existing concrete substrate. Most of the literature reported in the field of repair reveals that dimensional incompatibility, drying shrinkage in particular, is one of the major problems of concrete repair. This paper addresses the problem of stress buildup in concrete repair in the form of a jacketed column resulting from moisture diffusion. As moisture evaporates from the external jacket into the surrounding ambience of known relative humidity, the hardened concrete column restrains free-shrinkage movement of the repair layer. As a consequence, primary tensile stresses are set up in the jacket caused by restrained shrinkage. The jacketed layer under increasing tensile stresses is also subjected to tensile creep deformation, which results in a stress field of reversed sense as that caused by restrained shrinkage. These secondary stresses caused by restrained creep serve to relieve the primary shrinkage-associated stress field, and, as a result, the net or total stress buildup is reduced. A nonlinear finite element model is used to obtain the time-dependent moisture loss profile in the jacketed column. This model is interfaced with a finite element-based two-dimensional stress analysis program called SHCPAN for computing time-dependent restrained shrinkage and creep stresses. For a typical column repair, numerical experiments are carried out to highlight the influence of both a sealed jacket/column interface and a porous interface on the stress buildup in the jacketed columns.

Microstructural composition of the hardened cement pastes are analyzed using nanoindentation and 29Si MAS NMR after curing time periods of 7 and 28 days. Two curing conditions, room condition (20°C with 0.1 MPa pressure) and an elevated condition (80°C with 10 MPa pressure) are prepared to hydrate cement pastes [water to cement (w/c) ratio of 0.45]. The degree of hydration of the cement paste quantified using nanoindentation was compared with that from 29Si MAS NMR. From nanoindentation of the hardened cement pastes, microstructural hydration products are characterized with respect to the corresponding modulus of elasticity. A hydration product, which has a relatively high modulus of elasticity over other known hydration products, was found in the hardened cement paste cured in elevated temperature and pressure. The effect of high pressure on the composition of the hydration product is discussed and it is hypothesized that the packing density of calcium-silicate-hydrate (C-S-H) might increase when a cement paste is hydrated under high temperature and pressure.

With the high global demand of oil and gas, oilfield companies are seeking resources in the unexplored areas by drilling wells to explore the potential reserves of oil and gas. The drilling process has become more challenging in these unexplored areas, especially at the high pressure and high temperature conditions (HPHT). A strong cement sheath is highly desired to ensure the durability and integrity of the wells to overcome these challenges. The cement slurry design and cementing job become more challenging especially when the process is carried out at the high pressure and high temperature conditions. Industry is always looking for the new material which can be stable at these extreme conditions and meet the requirement effectively and economically. Polymer fibers are being used in the petroleum industry lately to assist in meeting these tough requirements. In this research, the usage of polypropylene fibers (PPF) on enhancing the oilwell cements properties at high pressure and high temperature (HPHT) were evaluated. The polypropylene fibers were added into cement admixture with discrete amount to evaluate its influence on enhancing the performance of cements especially those relate to the toughness. Experiments were performed using distinct cement slurry characteristics such as rheological properties, thickening time, compressive strength, density, porosity and permeability. The Scanning Electron Microscope (SEM), and X-ray powder diffraction (XRD) was also performed for analyzing the microstructure of the cement. The experimental tests showed that addition of fibers improves the mechanical properties, accelerates the thickening time, reduces the porosity and permeability and helps in designing a new cement slurry which withstands the HPHT conditions. Polypropylene fiber has a significant effect on reducing the porosity and the permeability of the base cement. Microstructural analysis showed that polypropylene fiber particles block the capillaries by filling the pores in the cement, so a dense cement structure is achieved.

Cementing is one of the most important and crucial issues in the oil field, especially for high pressure and gas bearing formations. It is difficult to achieve a good zonal isolation in such formation types, where pressure is abnormal and formation fluid contains corrosive fluids and gases. A common problem associated with highly over-pressurized zones is cross-flow after cementing. Fluid flow from an over-pressured zone to a low-pressure, high-permeability zone can lead to deterioration of the existing production hardware. Work over operations that attempt to repair cement voids — including: perforation, squeezing and use of casing patches or scab liners — are not recommended, as they do not provide long-lasting results. In one onshore field in Saudi Arabia, there was a problem related to cementing at high pressure zones. Recently, communication between A (abnormally over-pressurized zone) and B (low-pressure zone) formations occurred due to long term sea water injection, and has resulted in production interruption in a few wells. This paper addresses the problem through investigating field practices, including: drilling, cementing, and completion. This study also reviews the field reports and cased hole logs. A three-month study was conducted to evaluate the effects of formation-A water on cement, where the cement was exposed to formation-A water under downhole conditions. The tests for permeability, mechanical properties TGA and EDXRF are presented, in addition to discussions of some of the preliminary findings.