Ma. Cruz Alonso

Bio: Ma. Cruz Alonso is an academic researcher. The author has contributed to research in topics: Silica fume & Aluminate. The author has an hindex of 2, co-authored 2 publications receiving 98 citations.

Microstructure development in mixes of calcium aluminate cement with silica fume or fly ash

Abstract: The most widely identified degradation process suffered by calcium aluminate cement (CAC) is the so-called conversion of hexagonal calcium aluminate hydrate to cubic form. This conversion is usually followed by an increase in porosity determined by the different densities of these hydrates and the subsequent loss of strength. Mixes of calcium aluminate cement (CAC) and silica fume (SF) or fly ash (FA) represent an interesting alternative for the stabilization of CAC hydrates, which might be attributed to a microstructure based mainly on aluminosilicates. This paper deals with the microstructure of cement pastes fabricated with mixtures CAC-SF and CAC-FA and its evolution over time. Thermal analysis (DTA/TG), X-ray diffraction (XRD) and mid-infrared spectroscopy (FTIR) have been used to assess the microstructure of these formulations.

Changes in concrete pore size distribution due to electrochemical chloride migration trials

Abstract: Concrete structures suffering reinforcement corrosion are starting to be rehabilitated by means of electrochemical techniques, such as cathodic protection, chloride extraction, and realkalization that, in some cases, involve the application of relatively large electrical potentials or currents. The generalized movement of the ions dissolved in the aqueous phase of pores leads researchers to think that microstructure of concrete can be altered. In this study, results are presented on the changes in the pore size distribution after penetration of chlorides driven by an electrical field (migration) in comparison with natural diffusion penetration. Results indicate that the application of an electrochemical treatment to a structure induces an increase in total porosity, because of the solution of precipitated phases initially located in the smallest capillary pores that, after some time, evolve to be found in the range of 5 micro m to 0.05 micro m.

Approximate migration coefficient of interfacial transition zone and the effect of aggregate content on the migration coefficient of mortar

Abstract: In this study, the electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. In order to investigate the effect of aggregate content on the chloride migration coefficient of mortar, specimens with different fine aggregate volume fractions were cast and tested. The chloride migration coefficient of mortar was determined experimentally as a function of the volume fraction of aggregate. The chloride migration coefficient of mortar is used to assess the dilution, tortuosity and interfacial transition zone (ITZ) effects of aggregate in the cement-based composites. A model modified from the Bruggeman theory for the migration coefficient of mortar is used, and the regression analysis is used to determine the approximate chloride migration coefficient of ITZ. Based on the experimental and regression analytical results, the approximate ITZ migration coefficient is 2.83, 1.76 and 1.55 times of the matrix migration coefficient for the ITZ with the thickness of 20, 40 and 50 μm, respectively.

Compressive strength and microstructure of alkali-activated fly ash/slag binders at high temperature

Abstract: This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results.

Microstructural modifications in Portland cement concrete due to forced ionic migration tests. Study by impedance spectroscopy

Abstract: The forced migration test has been used during the last decades as an accelerated and useful method for determining the resistance of concrete to chloride ingress. Furthermore it allows to determine transport parameters of chloride ions through porous materials. The application of electric fields seems to introduce variations in the microstructure of concrete. In this work these variations have been studied using the impedance spectroscopy technique in the high frequency region (1 kHz–1 MHz). The results show that the dielectric response of concrete is also strongly modified during the migration experiments. The variations of the dielectric parameters during the migration tests can be explained in terms of modifications of the microstructure of concrete. The observed modifications are in good agreement with the results of mercury porosimetry analysis.

Microstructural investigation of calcium aluminate cement-based ultra-high performance concrete (UHPC) exposed to high temperatures

Abstract: This study investigated the microstructural and chemical changes of calcium aluminate cement (CAC)-based UHPC exposed to high temperatures. Upon exposure to 100 °C, C3AH6 was formed by the dehydration of CAH10. A further increase in the exposure temperature to 450 °C resulted in the formation of a new phase C12A7, which is attributed to the dehydration of C3AH6 and AH3. The compressive strength of UA50 and UA70 increased significantly due to the formation of C-A-(S)-H gel resulting from the further hydration of anhydrous CAC and silica fume upon exposure to 450 °C. The hydration reaction of CAC in UHPC led to a significant increase in the micro-pores (

Stabilisation/solidification of municipal solid waste incineration fly ash by phosphate-enhanced calcium aluminate cement.

Abstract: Landfill disposal of municipal solid waste incineration fly ash (MIFA) presents significant environmental and economic burden. This study proposed a novel and high-efficiency approach for stabilisation/solidification (S/S) of MIFA by phosphate-modified calcium aluminate cement (CAC). Experimental results showed that the presence of Pb (the most leachable metal contaminant in the MIFA) retarded the early-stage reaction of CAC, resulting in an extension of setting time and a significant decline of compressive strength of CAC pastes. The incorporation of phosphate additives (10 wt% of binder), especially for trisodium phosphate, in CAC system effectively mitigated the negative impact of Pb on the CAC reaction and reduced the Pb leachability. Elemental mapping results illustrated that Pb2+ coordinated with phosphate to generate insoluble precipitates (e.g., Pb3(PO4)2). The S/S treated MIFA samples fulfilled the compressive strength and leachability requirements for on-site reuse. Overall, this study demonstrated that phosphate-modified CAC is a promising binder for S/S of hazardous MIFA.