Engineered cementitious composites (ECCs) are potentially useful structural reinforcement and repair materials. However, owing to their high costs and carbon emissions, they are not used extensively. To control these carbon emissions and costs, recycled fly ash cenospheres (FACs) and high-strength polyethylene (PE) fibers are used here to explore the possibility of developing green lightweight ECCs (GLECCs). A series of experiments was conducted to test the physical and mechanical properties of the developed GLECC and to evaluate the possibility of developing an GLECC. The crack width development of the GLECC was also analyzed using the digital image correlation method. The experimental results indicate the following: (1) The increase in FAC content and the decrease in PE content worsened the performance of GLECCs, but the resulting GLECCs still had significant strain-hardening properties; (2) The performance and costs of GLECCs can be balanced by adjusting the amount of FAC and PE. The maximum amount of FACs attainable is 0.45 (FAC/binder), and the required amount of PE fibers can be reduced to 1%. As a result, the cost was reduced by 40% and the carbon emission was reduced by 36%, while the compressive strength was greater than 30 MPa, the tensile strength was greater than 3.5 MPa, and the tensile strain was nearly 3%. (3) The width of the crack was positively correlated with the FAC content and negatively correlated with the fiber content. In the 0.8% strain range, the average crack width can be controlled to within 100 μm and the maximum crack width can be controlled to within 150 μm, with the performance still meeting the requirements of many applications.

Carbonate manufactured sand (crushed sand from natural rock) offers an alternative to river and quartz sands in ultra-high-performance concrete (UHPC). This study compared calcite–dolomite sand with calcite-dominated sand. X-ray diffraction and fluorescence characterized mineralogical and chemical compositions. Total organic carbon analysis assessed apparent adsorption of a polycarboxylate ether superplasticizer (PCE). Flowability, fresh rheological properties, strengths, and cross-sectional visible porosity were evaluated at water-to-binder (w/b) ratios of 0.17, 0.16, and 0.15. The calcite–dolomite sand showed a 2.23% higher gradation-weighted apparent PCE adsorption index than the calcite-dominated sand. At w/b = 0.15, UHPC containing calcite–dolomite sand had a 6.45% lower flow spread, a 61.7% longer T500, a 17.5% higher dynamic yield stress, a 21.5% higher plastic viscosity, and a 7.0% higher visible pore area fraction than UHPC containing calcite-dominated sand. At matched w/b ratios, UHPC containing calcite–dolomite sand had 2.3–2.9% lower compressive strength than UHPC containing calcite-dominated sand; the flexural strength deficit increased from 8.0% to 16.0% as w/b decreased. Greater apparent PCE adsorption by sand may reduce dispersant availability, weaken particle dispersion, and impede air release through increased viscous resistance at low w/b ratios. A source-dependent effective PCE dosage window is proposed as a conceptual framework.