Civil and Environmental Engineering

We report here, for the first time in the literature, a method to synthesize hydrophobic and superhydrophobic concrete. Concrete is normally a hydrophilic material, which significantly reduces the durability of concrete structures and pavements. To synthesize water-repellent concrete, hydrophobic emulsions were fabricated and applied on portland cement mortar tiles.

Granulated blast furnace slag (GBFS) cement, containing up to 60% slag, is sometimes used in repair materials applied at intermediate temperatures of 150-300 8C. Low rate of strength development, especially at early ages, is considered a common disadvantage of repair mortars based on slag cement. The present research was oriented to improving a GBFS-portland cement binder for application as a repair material in the chemical industry when high thermal or acid resistance is required. It was found that the enhancement of GBFS-portland cement-based materials can be achieved with the help of silica fume (SF) and a superplasticizer (SP). The effect of different SPs on the compressive and flexural strength of SF-blast furnace slag-portland cement mortars was investigated. These mortars, in addition to high strength, demonstrate high thermal and acid resistance. D

This paper describes the exploration of a sensor concept for use in structural health monitoring. The sensor is based on the principle of electromagnetic (EM) surface wave propagation, and consists of a thin-layer of wave-guiding media attached to a metal base (e.g., steel bridge elements) and an EM wave emitter and receiver. Targeting at a low-cost and practical solution, various dielectric materials that facilitate EM wave propagation were examined. Low-density polyethylene was determined to have the most suitable dielectric properties and was selected for laboratory tests using tension coupon specimens.

The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nanocement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture is investigated. Experimental results demonstrate an increase in the compressive strength of mortars with SiO 2 nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer is proposed to facilitate the distribution of nano-SiO 2 particles. The application of effective superplasticizer and high-speed dispergation are found to be very effective dispersion techniques that improve the strength of superplasticized portland cement mortars, reaching up to 63.9 MPa and 95.9 MPa after aging during 1 and 28 days, respectively. These values compare favorably with the observed compressive strengths of reference portland cement mortars of 53.3 MPa and 86.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain the composite materials with improved performance.

The term ''icephobicity'' has emerged in the literature recently. An extensive discussion took place on whether the icephobicity is related to the superhydrophobicity, and the consensus is that there is no direct correlation. Besides the parallel between the icephobicity and superhydrophobicity for water/ice repellency, there are similarities on other levels including the hydrophobic effect/hydrophobic interactions, mechanisms of protein folding and ice crystal formation. In this paper, we report how ice adhesion is different from water using force balance analysis, and why superhydrophobic surfaces are not necessary icephobic. We also present experimental data on anti-icing of various surfaces and suggest a definition of icephobicity, which is broad enough to cover a variety of situations relevant to de-icing including low adhesion strength and delayed ice crystallization and bouncing.

The Compaction Packing Model was employed to calculate the packing densities of concrete. Nanomaterials extends the size range of particulate matter in fresh concrete. CNF at 0.04 vol.% of concrete account for 9% of the packing density of UHPC.

Fly ash has been effectively used for many years in producing high performance concrete, with limited use in asphalt pavements. This is possibly because the performance benefits that fly ash provides to asphalt mixtures are under-investigated. The reported research investigated the interaction of fly ash with different types of asphalt binders and documented important improvements found in the critical properties of asphalt. Microstructural investigation demonstrated in previous work, that crack-arresting behavior was successfully induced by evenly distributed fly ash particles within the bitumen matrix. Investigation of the rheological performance of blends of asphalt binders with different types of ash using dynamic shear rheometer confirmed the feasibility of using fly ash to improve the performance of asphalt 2 binders. Research data demonstrated increased resistance to oxidative aging. A longer service life could now be feasible due to increased resistance to mechanical and environmental loading.

This study investigated the effect of mechano-chemical activation (MCA) of superplasticized portland cement slurries on the performance of nano-engineered cement (NEC). Different parameters of MCA, such as the duration of activation and the composition of activated mix, were evaluated. Due to intensive milling and hydration, the mechano-chemically activated cement slurry (AC) contained up to 20% of nano-sized phase composed of superfine cement grains coated with products of hydration, mainly, C-S-H and ettringite. Different quantities of AC (at 10-20% cement replacement) were evaluated in NEC mortars. The microstructural characterization of NEC and the effects of AC were performed using XRD and SEM, and the compressive strength of NEC with different dosages of AC was tested. The research demonstrated that the use of MCA and application of activated cement in NEC increases the cement hydration rates and improves the mechanical properties of NEC-based mortars.

The term ''icephobicity'' has emerged in the literature recently. An extensive discussion took place on whether the icephobicity is related to the superhydrophobicity, and the consensus is that there is no direct correlation. Besides the parallel between the icephobicity and superhydrophobicity for water/ice repellency, there are similarities on other levels including the hydrophobic effect/hydrophobic interactions, mechanisms of protein folding and ice crystal formation. In this paper, we report how ice adhesion is different from water using force balance analysis, and why superhydrophobic surfaces are not necessary icephobic. We also present experimental data on anti-icing of various surfaces and suggest a definition of icephobicity, which is broad enough to cover a variety of situations relevant to de-icing including low adhesion strength and delayed ice crystallization and bouncing. T he terms ''icephobic'' and ''icephobicity'' have been used in the literature recently 1-11 , although the words are relatively new and still absent from the Oxford English Dictionary. The keyword ''icephobic'' was used for the first time by Kulinich and Farzaneh 3 as well as in some industrial reports 12,13. Next time, in the form ''ice phobic,'' it appears in 2008 in the work done at NASA 14. After that, the term appears many times in the literature. The term is analogous to the hydrophobicity and other ''-phobicities'' (oleophobicity, lipophobicity, omniphobicity, amphiphobicity, etc); however, an exact thermodynamic definition of icephobicity is missing from the literature. The extensive controversy among scholars on whether the icephobicity is related to the superhydrophobicity came to a conclusion that there is no direct correlation 5-7. In recent publications there are at least three different approaches to the characterization of surface icephobicity. First, icephobicity implies low adhesion force between ice and a solid surface. In most cases, the critical shear stress is calculated, although the normal stress is used as well. The researchers call ''icephobic'' surfaces with the shear strength between 150 kPa and 500 kPa 2,15 and even as low as 15.6 kPa 16. Second, some scholars define icephobicity as the ability to prevent ice formation on the surface. Such ability depends on whether a droplet of supercooled water (below the normal freezing temperature of 0uC) freezes at the interface and it can be characterized by time delay of heterogeneous ice nucleation 5,17,18. The mechanisms of droplet freezing are quite complex and depend on the temperature level, on whether cooling is performed from the side of the solid substrate or from vapor, and on other factors. Third, an impact test for bouncing-off droplets was suggested 4 implying that icephobic surfaces repel incoming small droplets (e.g., of rain or fog) at the temperatures below the freezing point. These three definitions of icephobicity correspond to three different, although related, properties of anti-icing surfaces: they should (i) prevent freezing of water condensing on the surface (ii) prevent freezing of incoming water (iii) if ice formed, it should have weak adhesion strength with the solid, so that it can be easily removed. Mechanical properties of ice and the substrate also of great importance since ice shedding occurs as fracture, either in the mode I (normal) or mode II (shear) cracking, so that crack concentrators are major contributors to the reduced strength 6. All of the above considerations suggest that a universal definition of the icephobicity can be a difficult task and the parallel with the superhydrophobicity should be examined in depth. The superhydrophobicity is defined by the water contact angle (CA). 150u and by low CA hysteresis 19,20 , although very high CA can co-exist with high CA hysteresis (the rose petal effect) 21. Low CA hysteresis corresponds to shear mode of loading at the solid-water interface while a high CA corresponds to the normal loading. The ability to bounce-off incoming droplets constitutes the third aspect of the superhydrophobicity 22. In the present paper, we will examine adhesion properties of ice in view of their parallelism with the above-mentioned properties of superhydrophobic materials.

ABSTRACTThis paper reports on the development of a new type of low cost artificial aggregates based on granulated reactive silica (AAGS) for application in lightweight concrete. The functional principle of AAGS is based on the formation of polysilicate solutions under heat treatment (up to 80 °C) and migration of these solutions into the porous space of concrete under the thermal gradients, resulting in strengthening of inter-porous space. Developed AAGSs are based on low cost local raw materials, which may contain different amounts of amorphous silica. The activity coefficient (AC) and amorphous silica content are used to evaluate the performance of raw materials by suggested accelerated method.Silica components with different genesis are investigated and ranked according to their AC. It is found out that chemogenic and biogenic siliceous rocks with a low degree of diagenetic transformations, which are mostly represented by CT-opals (a low-temperature nanoscale modification of trid...