Journal of Materials in Civil Engineering

Temperature is known to be one of the most important factors affecting the design and performance of asphaltic concrete pavement. For a successful pavement design, it is vital to know the range of temperatures over which a pavement will be subjected. This is especially true for desert climates. Trends in solar radiation, air temperature, surface temperature, and temperature at different depths were measured for a 25‐cm coastal slab as well as 15 cm, 20 cm, and 30 cm inland slabs in the arid Saudi coastal and inland environment. Data were analyzed for seasonal and daily variations. Surface temperature was found to be less than the temperature at a depth of 2 cm only for hot summer months and at hours of high solar radiation. Pavement temperatures ranged between 3°C and 72°C for coastal slab, and between 4°C and 65°C for inland slabs. This wide range of temperature variation results in drastic variation of asphalt concrete modulus. As temperature increases from 30°C to 60°C, the resilient modulus reduces from 5,500 MPa to 800 MPa.

The compressive strength of 70‐, 120‐, 200‐, and 250‐mm concrete cubes, subjected to four different curing regimes, was determined at the ages of 28 and 90 days, in order to study the influence of specimen size on the effect of curing regimes on cube strength. In the first curing regime the specimens were exposed unprotected to 30°C/40% RH. The second regime was similar to the first one but exposure took place at 20°C/65%. In the third regime the specimens were stored in water at 20°C to the age of seven days followed by storage in air at 20°C/65%, and in the fourth regime the specimens were continuously stored in water at 20°C. It was found that the effect of curing regimes on cube strength is related to specimen size, and it is much greater in the smaller than in the larger specimens. For example, the 28‐day strength of the concrete subject to seven days wet curing (third regime), was about twice the strength of the corresponding uncured concrete when 70‐mm cubes were tested, and only 10% greater when 250‐mm cubes were tested. Test results also include data on the effect of moisture content on cube strength and on the effect of specimen size on strength development between the ages of 28 and 90 days.

The disposal of sewage sludge for modern municipalities represents an ever‐increasingly difficult problem. Feasibility studies on the use of sludge to produce cement as a means of ultimate sludge disposal has been initiated. Various properties of the cement, which include chemical compositions and physical properties, as well as mortar strength, are examined. The experimental study indicated that the so‐called biocement that derived from sewage sludge exhibits adequate strength for general masonry work. Laboratory tests were carried out to examine the use of biocement as a partial replacement material for Portland cement. The results show that the biocement can replace up to 30% by weight of ordinary Portland cement without deteriorating the mortar strength. Blended cement with up to 10% replacement level not only shows higher strength than control Portland cement, it also exhibits higher rate of strength development at early ages. Properties of both the biocement and the resulting blended cements are presented in this paper.

A stochastic model has been developed for simulating correlated nonstationary spatial variation of modulus of elasticity (MOE) and parallel to grain compressive strength $\left({\sigma }_c\right)$. Two grades of $38\times 89\mathrm{mm}$ spruce‐pine‐fir machine stress‐rated lumber, 2400f‐2.0E and 1650f‐1.5E, have been tested to obtain within‐member MOE and ${\sigma }_c$ profiles. Each piece, 4.88‐m long, has been cut into 152‐mm segments where within member ${\sigma }_c$ values have been obtained. Test results have revealed that the within‐member MOE and ${\sigma }_c$ profiles are correlated and nonstationary. The data have been used to develop and verify a stochastic model. Trend‐removal techniques, spectral representation method, bivariate standard normal simulation model, and moving‐average model have been used to generate within‐member MOE and ${\sigma }_c$ profiles. The correlation structure and nonstationary characteristics of the MOE and strength profiles have been preserved. Good agreement has been obtained between model predictions and test data.

The optimum drying temperature of concrete prior to monomer impregnation was investigated. Mortar cubes were cast, dried at different temperatures between room temperature and 316°C (600°F), and impregnated with monomer and polymerized in situ. The cubes were then vacuum‐saturated and their resistivities were measured. The cubes were cut and dried to 104°C (220°F), and the influence of drying temperature on the degree of impregnation was evaluated using a mercury porosimeter and a scanning electron microscope‐energy dispersive spectroscope. Companion cubes were subjected to ponding‐drying cycles in a sodium chloride solution, and the ingress of chloride was determined from powdered samples. Results were used to optimize the drying temperature of concrete for monomer impregnation. The results demonstrated that monomer impregnation of concrete to a desired depth can be achieved at a lower temperature than previously believed.

Dolomite $\left[\mathrm{CaMg}\right({\mathrm{CO}}_3{)}_2]$ slabs were exposed to 8.0, 14.05, and 20.88 ppm ${\mathrm{SO}}_2$ atmosphere in several experiments, and the conversion‐time data were evaluated in terms of the random pore model proposed by Bhatia and Perlmutter (1980). The pore volume, pore surface area, and the pore length required for the application of the model were estimated from the mercury intrusion porosimeter measurements. The experimental conversion‐time data were fitted to obtain the surface reaction rate constant as $4.90\times {10}^{-6}{\mathrm{cm}}^{2.98}/{\mathrm{mmol}}^{0.66}h$ and the reaction order as 0.66. With the help of these two reaction parameters, it was possible to predict the porosity increase due to reaction. Results compare well with experimental values.

Development of pavement concrete compressive strength, flexural strength, and splitting tensile strength as a function of time is discussed. Eighteen sets of post‐1985 exerimental data from academic and industrial sources were selected to form a database of strength data for “modern” pavement concrete. Specimens were categorized as high or normal strength, use of fly ash was identified, and curing conditions were noted. Significant gains beyond 28‐day strength are observed in compressive, flexural, and tensile strength of modern pavement concretes. This general observation holds true for high‐ and normal‐strength concrete, concretes with and without fly ash, and concretes cured in air and moist conditions. Modern concretes have higher early compressive strength gains than concretes produced in 1940–56. However, both modern and 1940–56 concretes exhibit similar long‐term trends in strength development when normalized to their 28‐day strengths.

An experimental investigation was carried out to determine the suitability of fiber‐reinforced cementitious composites containing high‐volume fractions of very fine (micro) fibers of carbon and steel for thin repairs. Two series of tests were performed: the first in which the fracture characteristics of the fiber‐reinforced composites themselves were assessed, and the second in which the bond developed between an old concrete substrate and fiber‐reinforced repair composite was determined by conducting tensile tests on cylindrical repair assemblies. Tests were conducted at 22°C and at −50°C in an environmental chamber. The fracture characteristic of cement matrices were considerably improved due to microfiber reinforcement. Significant improvements in the repair bond strength value due to fibers were also noted. The test data clearly demonstrate the potential of microfiber‐reinforced cement‐based composites as a thin repair material.

Within the general framework of developing a cement‐based sandwich panel for housing construction, wood‐cement composites were identified as a promising facing material. Five commercially available wood‐cement and natural‐fiber‐cement board products were studied in an experimental program. The modulus of elasticity, the limit of proportionality stress, the modulus of rupture, and the post‐cracking behavior were measured in three‐point bending. The compressive strength and failure mode were characterized from uniaxial compression tests on small cubic specimens. The microstructure of these composites was characterized using a scanning electron microscope. The effect of the fiber reinforcement on the mechanical properties was related to the observed behavior.

The writers present the results of research findings on the micro‐structural development in a high‐volume fly‐ash (HVFA) cement system containing 60% fly ash by weight of binder. Although the one‐day strength of HVFA mortar is low compared to plain cement mortar, from three‐day onward the strength starts to increase. Corresponding to the development of microstructure, the strength increases significantly at later ages and reaches 78% of the control specimen at 180 days. The literature survey reveals that hydration of fly‐ash aluminate phases produces hydrates similar to those in cement. To reveal the fly‐ash hydration process more vividly, a special type of cement containing very low $C_{3}A$ and alkalies was used with a class F fly ash. In order to precisely determine the role of high‐volume replacement in a cementitious system, a comparative study of plain cement and HVFA paste was carried out. The mechanism of fly‐ash hydration in this system is discussed and a correlation between its microstructure/strength development established. Better dispersion of cement grains, smaller $\mathrm{Ca}(\mathrm{OH}{)}_2$ crystals, and formation of more gel phases largely account for the strengthening effect. The effect of fly‐ash replacement on neat water‐to‐cement ratio, initial pore content, $\mathrm{Ca}(\mathrm{OH}{)}_2$ crystallization, and dissolution of fly‐ash glass phase are discussed. Comparison of experimental results determined by x‐ray diffraction (XRDA) analysis, strength measurement, and thermogravimetry/differential thermal analysis (TG/DTA) is also presented.

In many pavement applications, asphalt concrete is exposed to damage from fuel spills or drippage. A fuel‐resistant sealer (FRS) is often required to protect the asphalt concrete pavement from possible damage. Coal‐tar emulsion mixtures with an aggregate added to provide for skid resistance is commonly used to protect the pavements. These mixtures or sealers often contain additive materials designed to improve sealer performance. The development of fuel‐resistant sealers and various additives and their effects on the performance of the sealers are discussed. Also discussed are procedures normally used for mixing and applying the sealers, materials, and proportioning and construction practices that can affect the field performance of these sealers. Recent research financed by several government agencies has sought improved methods for specifying and testing coal‐tar sealer mixtures. The methods currently used for specifying and testing these mixtures and the needs of user agencies are discussed.

The structural behavior of steel‐reinforced polymer concrete (PC) beams using unsaturated polyester resin binders based on recycled polyethylene terephthalate (PET) plastic waste is evaluated. Steel fibers are also used in some of the beams. The investigation includes load‐deflection and moment‐curvature responses, modes of failure, cracking patterns, variation of neutral axis depth with loads, strength properties, ductility index, the effect of tensile reinforcement ratio on the flexural strength of PC beams, and the effects of shear span‐to‐depth ratio, tensile reinforcement, and compressive strength on the shear strength of PC beams. The ultimate flexural strength of reinforced PC using resins based on recycled PET is compared to other reinforced concrete systems. The effects of steel fibers on the load‐deflection response and shear strength of reinforced PC beams are also evaluated. Resins using recycled PET offer the possibility of producing very good quality PC at a lower cost for structural applications. Also, the recycling of PET in PC helps in saving energy and in partially solving a solid waste problem posed by plastics.