The key points to check are the fineness modulus, particle size distribution, mud content, clay lump content, moisture content, and impurities of the sand. The sand should first be visually inspected for mud content, clay lump content, and other indicators to make a preliminary judgment on the quality of the sand, mainly by "looking, pinching, rubbing, and polishing" .
"Looking" – grab a handful of sand and spread it in your palm, then carefully examine the uniformity of the distribution of coarse and fine sand particles. The more uniform the distribution of each particle size, the better the quality.
"Pinching" is used to determine the moisture content of sand by pinching it with your hands. After pinching, observe the tightness of the sand ball. The tighter the sand ball, the higher the moisture content, and vice versa.
"Rubbing" involves taking a handful of sand and rubbing it between your palms. Then, gently pat your hands and observe the layer of mud adhering to your palms. The more mud layer there is and the more yellow it is, the higher the mud content of the sand. Conversely, the lower the mud content, the lower the mud content.
"Tossing" refers to tossing the sand in your palm after kneading it. If the sand clump does not break apart, it can be determined that the sand is fine and contains a lot of mud or water.
II. Gravel
The key points of inspection include the stone's specifications, particle size distribution, mud content, mud lump content, needle-like and flaky particle content, and impurities, mainly relying on visual methods such as "looking" and "grinding".
"Looking" involves observing the maximum particle size of the crushed stone and the uniformity of the distribution of different particle sizes. This allows for a preliminary assessment of the quality of the crushed stone gradation. The amount of needle-like and flaky particles can estimate the impact of the crushed stone on the workability and strength of the concrete. The thickness of dust particles adhering to the surface of the crushed stone can indicate its mud content. The distribution of grains on a clean surface of the crushed stone, combined with "grinding" (grinding two pieces of crushed stone together), can analyze the hardness of the crushed stone. Check for shale and yellow clay particles in the aggregate. If there are many shale particles, the aggregate is unusable. Yellow clay particles fall into two categories: those with water stains but no mud are usable and will not affect the bond between the aggregate and mortar. Particles with yellow mud adhering to their surface are the worst quality; they significantly affect the bond between the aggregate and mortar, and a large number of these particles will reduce the compressive strength of the concrete.
III. Admixtures
The visual inspection of concrete admixtures provides a preliminary method for identifying their chemical composition. By observing the color, one can roughly differentiate between naphthalene-based admixtures, (SNF) which typically exhibit a brown hue and polycarboxylic acid types(PCE), which are generally colorless or pale yellow. Additionally, some products are blends of naphthalene-based and aliphatic admixtures, often presenting a reddish-brown shade.
Beyond color, the odor of the water-reducing agent can also serve as an indicator for determining its type. This simple yet effective approach offers an accessible means for initial quality assessment before more detailed chemical or performance testing.
IV. Supplementary Cementitious Materials (SCMs)
The sensory quality of fly ash is mainly determined by the simple methods of "looking, pinching, and washing"
"Looking" refers to observing the particle shape of the fly ash. If the particles are spherical, it indicates that the fly ash is the original duct ash; otherwise, it is finely ground ash.
"Pinching" involves pinching the fly ash between your thumb and forefinger to feel the smoothness between your fingers. The smoother the ash, the finer the fly ash; conversely, the coarser the ash, the less smooth it is.
"Washing" involves grabbing a handful of fly ash, squeezing it, and rinsing it with tap water. If the residue adhering to the palm of the hand is easily rinsed off, it can be judged that the fly ash has a low loss on ignition. Conversely, if there is a lot of residue that is difficult to rinse off, it indicates that the fly ash has a high loss on ignition.
The appearance and color of fly ash can also indirectly reflect its quality. A darker color indicates a higher carbon content and a greater water requirement. In case of abnormalities, a mix design test should be conducted promptly to check the impact on water consumption, workability, setting time, and strength.
Slag powder is white in appearance. If the slag powder is gray or black, it means that it may have been mixed with steel slag powder or fly ash with low activity.
