The present work is a study on alkali activation of Mexican blast furnace slag, using sodium silicate. The aim is to produce an optimal specimen, homogeneous without carbonation, and with small fraction of crystalline phases, similar to CSH, which provide mechanical properties suitable to use in the construction industry. The samples were prepared using sodium silicate activator solutions with modulus (SiO2/Na2O) of 1.25, 1.5, and 1.75. The weight percentage of Na2O in the activator solutions was added at 4, 6 and 8% relative to the slag weight. The prepared samples were stored in sealed molds, at room temperature (20°C), during 7 days. The X-ray diffraction has revealed the presence of an amorphous phase, semi crystalline clinotobermorite phase and signals of calcium carbonate for the samples of 4 and 6 % of Na2O; in contrast with the 8% Na2O, where the latter signals almost disappeared. The specimen selected as optimal was prepared with an activator concentration of 8% of Na2O /Slag, and SiO2/Na2O of 1.25. A specimen under these optimal conditions was prepared with accelerated curing (40°C, humidity, 48 hours), and a compressive strength test was attained, with an average value of 52 MPa at 3 days.

This paper focus on evaluating the ability to use Mexican fly ash (FA) and copper slag (CS) to produce alkali cements (0% OPC) or hybrid cements (20% OPC + 80% fly ash). The alkali activators used were two: 8 M NaOH solution for alkali cements and NaCl with sodium silicate for hybrid cement (HYC). Results of mechanical testing and characterization of the reaction products formed after 2 and 28 days are presented and discussed. Mechanical strength in some cases exceeded 20 MPa, at 2 days curing. The chemical characterization techniques used were X-Ray Diffraction (XRD) and scanning electron microscopy (SEM).

Tensile strength of concrete is limited and therefore is sensitive to crack formation. Steel reinforcement is added to bear the tensile forces; nonetheless, this does not completely omit crack formation. Repair of cracks in concrete is time-consuming and expensive. Self-sealing and self-healing of cracks upon appearance would therefore be a convenient property. We propose a mechanism to obtain self-repair of the concrete by adding soluble silicates (ASS) which will induce a self-sealing and self-healing process catalyzed by natural periods of wet and dry states of the concrete. Self-sealing approaches prevent the ingress of harsh chemical substances which may deteriorate the concrete matrix. This can be achieved by self-healing of concrete cracks (e.g. further cement hydration, calcium carbonate precipitation) and autonomous healing (e.g. further hydration of partially soluble silicates added as healing agents). The autogenous healing efficiency depends on the amount of deposited reaction products (ASS), its solubility (ratio of calcium to sodium silicate), the availability of water, and the crack width (restricted by adding microfibers). The self-sealing efficiency is generally evaluated by measuring the decrease in water permeability and air flow through the crack. The healing efficiency is usually evaluated by testing concrete´s regain in mechanical properties after crack formation; by reloading the cracked and autonomously healed specimen and comparing the obtained mechanical properties with the original ones. Self-sealing and self-healing of concrete gives a broad perspective and new possibilities to make future concrete structures more durable.

Synthetic superabsorbent polymers (SAPs) are used in concrete for various applications such as internal curing and frost resistance. However, the addition of these SAPs may lead to a significant decrease in mortar strength, especially when high amounts of SAP are necessary. This is the case for example when self-sealing and -healing of cracks is strived at. In order to overcome this bottleneck, the present work focuses on the application of biopolymers as SAPs. The work especially aims to evaluate the potential of both sodium alginate (NaAlg) as well as physically cross-linked calcium alginate (CaAlg) as SAPs to establish a sustainable approach towards self-sealing and -healing concrete without impairing mechanical strength. First, the swelling properties in both demineralized water and cement filtrate solution are tested. Subsequently, the mechanical properties of mortar mixtures in the absence and the presence of SAPs are compared by performing flexural and compressive tests. The alginates show a swelling capacity up to 72 times their own weight in aqueous solutions. Interestingly, they lead to a minor reduction in compression strength (up to 15% upon addition of 1m% SAP). These biopolymers show high potential for enabling concrete repair, more specifically, for the self-sealing and -healing of cracks without impairing the strength.

Several experimental efforts related to the concrete improvement are focused to increase its flexural strength to complement the high compressive strength, which is usually developed by materials of this nature. The flexural strength or modulus of rupture of the concrete is important in civil engineering applications such as infrastructure projects, pavements and buildings. This work proposes an alternative to optimize concrete flexural strength through the functionalization of the 9 Angstrom (Å) Tobermorite using Carbon Nanotubes (CNT). A complete ab-initio, 3D Atomistic Model of the 9Å Tobermorite is presented as the basis of the silicate cementitious hydrated products. In order to validate the model, some mechanical properties were computed using a Density Functional Theory (DFT) based program. Afterwards, a functionalization based on CNTs with different diameters was carried out to improve the flexural strength of the concrete.

The current work reports the effect of particle size on the rheological behavior of polymer modified asphalt PMA. The modified asphalt was generated with AC-20 asphalt precursor provided by Pemex Salamanca and Solprene® 416 provided by Dynasol Mexico. Solprene® 416 is a SBS star-type copolymer with 4 poly(b-styrene-b-butadiene) arms and Mw = 2.36X105 g/gmole. Modified asphalt samples were prepared with 3 wt % of SBS via hot mix process. Mixing time and temperature were kept constant at 4h and 180 °C. This study also varied the agitation in the mixing process: 500, 1000 and 1500 rpm. All PMAs shown sphere-shaped polymer particles as observed via fluorescent microscopy using a Carl Zeiss KS-300 system. Base asphalt and PMAs were also characterized through rheological measurements using a TA Instruments AR-G2 rheometer. Shear viscosity (η) and tan δ data shown that the flow resistance of the PMA increases as the size its polymer particles decreases. Since the size of the polymer particles decreases with the increase of the stirring speed, it is concluded that the stirring speed of the process determines the size of the polymer particles and so the mechanical resistance of the PMA.