A Wine-Derived Acid Slows Cement, Then Makes It Stronger

Cement is one of the most familiar materials on Earth, yet its inner chemistry still hides surprises. In a study published in Case Studies in Construction Materials, researchers report that a tiny dose of L-(+)-tartaric acid, the same hydroxycarboxylic acid found naturally in grapes and wine, can transform how Portland cement hardens. At just 0.15 percent of the cement mass, the compound delayed early setting, reshaped the growth of key crystals, refined the pore network, and ultimately delivered the highest flexural and compressive strengths measured across the tested dosages. The finding matters because retarding admixtures are essential tools for controlling workable time during mixing, transport, and placement, but their influence does not stop at the fresh state. What happens in the first hours of hydration echoes through weeks of microstructural evolution, and the new work traces that chain of cause and effect with unusual completeness across a single, consistent binder system.

The research team, led by Borui Lu, Yue Wang, Peiyao Yu, Mingzhe An, Ziruo Yu, and Yu Zhang, investigated L-(+)-tartaric acid at dosages of 0, 0.10, 0.15, and 0.20 percent of cement mass, holding the water-to-cement ratio fixed at 0.40 and using a fixed polycarboxylate superplasticizer dosage of 0.02 percent to keep the admixture background constant. They paired two parallel series: aggregate-free cement pastes for setting time, thermogravimetric analysis, X-ray diffraction, and electron microscopy, and one-to-three cement-to-sand mortars for fluidity, mercury intrusion porosimetry, and mechanical testing. This paired design allowed the same chemical perturbation to be followed from paste-scale hydration chemistry through to mortar-scale pore structure and strength. Specimens were cured at 20 degrees Celsius and above 95 percent relative humidity and examined at 7, 28, and 56 days, giving a cross-age picture that most earlier tartaric acid studies, which focused on early hydration alone, did not attempt.

The fresh-state results show a textbook dosage response. Both initial and final setting times increased continuously as the tartaric acid dose rose, with the delay becoming steep at the higher dosages. Mortar fluidity followed the same pattern: the flow-table spread grew from 214 millimeters for the control mix to 242 millimeters at 0.20 percent, an increase of about 13.1 percent under the fixed superplasticizer dosage. Because cement setting occurs when hydration products connect neighboring particles into a load-bearing network, the measured delay points directly to a longer period before that network reaches percolation. The authors interpret the combined setting and flow data as progressively stronger early-age retardation, consistent with a molecular picture in which tartrate ions coordinate calcium in solution and adsorb on clinker and hydrate surfaces, modifying dissolution and the conditions required for calcium silicate hydrate nucleation.

Quantitative X-ray diffraction with Rietveld refinement, using a 50 percent corundum internal standard and a common constrained five-phase protocol across all twelve datasets, provided an independent marker of the same trend. At 7 days, residual C3S, the reactive alite phase that drives early strength, rose systematically from 13.45 percent in the control paste to 17.33, 19.53, and 20.35 percent at the 0.10, 0.15, and 0.20 percent dosages respectively. Residual beta-C2S showed a much weaker dosage trend, indicating that the retardation acts primarily on alite. By later ages, residual C3S declined in all mixtures, demonstrating that silicate consumption continued after the strongly retarded early stage rather than being permanently suppressed. This distinction between delayed and diminished hydration is central to the study’s argument that retardation can be a benefit rather than a penalty.

Portlandite, the crystalline calcium hydroxide that cement hydration produces in abundance, served as a second chemical record. Thermogravimetric analysis, quantifying portlandite from the dehydroxylation mass loss between 400 and 550 degrees Celsius, showed contents falling monotonically at 7 days from 18.75 percent in the control to 18.01, 16.26, and 14.43 percent with increasing dosage. Yet by 56 days the picture had inverted: the 0.10 and 0.15 percent pastes reached 22.58 and 23.12 percent portlandite, exceeding the control’s 21.12 percent. The quantitative XRD data mirrored this early suppression and later recovery, and the agreement between the two independent techniques at 7 days provides a cross-method consistency check. The divergence in absolute values at later ages reflects the different analytical signals involved, mass loss versus diffraction intensity, and the authors interpret each dataset within its own measurement basis.

Scanning electron microscopy with energy-dispersive X-ray spectroscopy added local chemical evidence for the microstructural story. A representative elongated plate-like crystal in the 0.15 percent paste at 7 days gave a calcium-rich composition with a calcium-to-silicon atomic ratio of about 3.55 and no detectable aluminum or sulfur, a signature compatible with portlandite once the silicon contribution from adjacent silicate hydrate within the interaction volume is considered. Across all dosages and ages, similar plate-like crystals appeared with dosage- and age-dependent changes in size, abundance, and spatial arrangement. This matters because portlandite habit is known to be sensitive to the chemical environment of growth: organic molecules can alter crystal number, size, and growth pattern, and dissolved ions can shift the relative stability of specific crystal faces. The tartaric acid environment thus appears to leave a legible fingerprint on the crystal architecture of the hardened paste.

The pore network of the corresponding mortars evolved in step with the phase history. Mercury intrusion porosimetry, interpreted in terms of pore-entry or threshold dimensions rather than true pore sizes, showed that for the 0.15 percent mortar, cumulative intrusion at the smallest displayed entry diameter of about 11 nanometers fell from 0.0395 milliliters per gram at 7 days to 0.0314 milliliters per gram at 56 days, a deficit relative to the control that widened from 9.6 percent to 22.2 percent. The principal differential peaks stayed within a narrow 32 to 40 nanometer band throughout curing, meaning the characteristic entry scale was stable while the accessible volume changed most. By 56 days the 0.15 percent mixture had the lowest cumulative intrusion of all four mortars, linking the sustained post-retardation hydration documented in the pastes to a progressively denser, less accessible pore network in the mortars.

Strength development crowned the sequence. Both flexural and compressive strengths increased as the dosage rose from zero to 0.15 percent and then declined at 0.20 percent, making the 0.15 percent mix the best performer at every age. Relative to the control, its flexural strength was higher by 20.0, 14.6, and 9.6 percent at 7, 28, and 56 days, while compressive strength exceeded the control by 33.7, 16.0, and 11.7 percent at the same ages. The advantage was largest at 7 days and narrowed as the control caught up in hydration, consistent with the established understanding that strength in hydrated cement is governed jointly by porosity, pore structure, and degree of hydration. Notably, the 0.20 percent mixture, despite showing the lowest early cumulative intrusion at 7 and 28 days, did not match the 0.15 percent strength, suggesting that excessive retardation leaves the hydration degree too far behind for pore refinement alone to compensate.

The study also raises an intriguing stereochemical question. Previous work on brushite bioceramics and calcium sulfate cements found that L-(+)-tartaric acid and other L-enantiomeric alpha-hydroxycarboxylic acids regulated crystal growth and enhanced mechanical performance more strongly than their D counterparts, identifying molecular handedness as a possible control variable in calcium-mineral crystallization. The present dataset characterizes only the L stereoisomer in ordinary Portland cement, so matched comparisons of L-, D-, meso-, and racemic tartaric acid systems remain an open experimental frontier. The authors likewise note that the portlandite observations connect plausibly to carbonation behavior, since both the amount and spatial form of calcium hydroxide influence how carbonation progresses, motivating future measurements of carbonation depth and dimensional change.

For now, the practical takeaway is a carefully bounded one. At a water-to-cement ratio of 0.40, 0.15 percent L-(+)-tartaric acid best balanced early hydration control with later hardened-state development, combining pronounced setting delay and improved flow with continued silicate consumption, the lowest late-age accessible pore volume, and the highest measured strengths. Because tartaric acid’s retarding action is strongly concentration-dependent, and because dosage expressed per cement mass translates into different effective concentrations in the mixing water at different water-to-cement ratios, the optimum window is expected to shift with mixture design. The authors caution that verification across other ratios and cement chemistries is needed before broader dosage recommendations can be made. Even so, the work demonstrates that a modest, wine-cellar-simple molecule, dosed with precision, can orchestrate the entire arc of cement hydration from first stiffening to final strength.

Subject of Research: Effects of L-(+)-tartaric acid dosage on hydration, microstructure, and strength development of Portland cementitious materials

Article Title: Hydration regulation, microstructural evolution and strength development of cementitious materials modified by L-(+)-tartaric acid

Article References: Lu, B., Wang, Y., Yu, P., An, M., Yu, Z., & Zhang, Y. (2026). Hydration regulation, microstructural evolution and strength development of cementitious materials modified by L-(+)-tartaric acid. Case Studies in Construction Materials, 25, Article e06609. https://doi.org/10.1016/j.cscm.2026.e06609

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06609

Keywords: cement hydration, tartaric acid, retarding admixture, portlandite, Rietveld QXRD, thermogravimetric analysis, mercury intrusion porosimetry, compressive strength, microstructure, C3S, pore structure, construction materials